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AN INTRODUCTION TO ENTOMOLOGY 



AN INTRODUCTION TO 

ENTOMOLOGY 



BY 

JOHN HENRY COMSTOCK 

LATE PROFESSOR OF ENTOMOLOGY AND GENERAL INVERTEBRATE 
ZOOLOGY IN CORNELL UNIVERSITY 



NINTH EDITION 
REVISED 




ITHACA X^^^ NEW YORK 
COMSTOCK PUBLISHING COMPANY, INC. 

1949 



COPYRIGHT 1920 BY 
COMSTOCK PUBLISHING COMPANY 



COPYRIGHT 1924 BY 
J. H. COMSTOCK 



COPYRIGHT 1933, 1936, 1940 BY 
COMSTOCK PUBLISHING COMPANY, INC. 



PRINTED IN THE UNITED STATES OF AMERICA BY 
THE VAIL-BALLOU PRESS, INC., BINGHAMTON, N. Y. 



TO 

MY OLD STUDENTS 

WHOSE YOUTHFUL ENTHUSIASM WAS A CONSTANT INSPIRATION 

DURING THE LONG PERIOD OF MY SERVICE AS A TEACHER 

THIS EFFORT TO CONTINUE TO AID THEM IS 

AFFECTIONATELY INSCRIBED 



PREFACE TO THE 1940 EDITION 

INCREASING interest in the biological control of insects has cre- 
ated an insistent demand for a wider knowledge of the parasitic 

forms active in destroying those insects which are injurious to 
agriculture. The greater number of these parasitic species is found in 
the order Hymenoptera. Opportunity has, therefore, been taken in 
this edition (1940) to revise and extend the discussion of the superf ami- 
lies Ichneumonoidea, Proctotrupoidea and Chalcidoidea, the groups 
which contain the most important parasites. In addition, a shorter 
key to the commoner families of the suborder Clistogastra together 
with keys to the subfamilies of the Ichneumonidae and Chalcididas 
have been included. 

The text for the keys and for the new matter on the parasitic 
Hymenoptera has been contributed by Dr. Henry K. Townes, who 
has given much study to these groups. It is hoped that the keys 
will prove helpful to those interested in the parasitic forms. 

Glenn W. Herrick 
Ithaca, June IQ40. 



PREFACE TO THE 1936 EDITION 

IT SEEMED opportune with this reprinting (1936) of the Intro- 
duction to make some slight revision, more specifically of the 

orders of the wingless insects. 

The class Myrientomata of Berlese has been advanced to its 
more logical position as the order Protura of Silvestri, under the 
Hexapoda. This has been done with some reservation, but in 
accord with the trend of opinion among morphologists and probably 
most systematists. 

Probably the data for treating the suborder Entognatha of the 
Thysanura as a definite order are more numerous and more reliable 
than for the foregoing change in position of the Protura. Out of 
respect, however, for the careful conservatism of Professor Comstock, 
the writer has retained the Entognatha as a subordinate group in the 
Thysanura. This is, no doubt, illogical because Professor Comstock 
always kept pace with legitimate progress in his field of science. 




PREFACE 

The Hemimeridae has been advanced to its place in the Dermap- 
tera and the discussion briefly extended on the basis of the paper by 
Rehn and Rehn. 

At the suggestion of Dr. J. C. Bradley the suborder Idiogastra 
has been abandoned and the family Oryssidae included among the 
Chalastogastra. 

Glenn W. Herrick 
Ithaca, July iQj6. 



THE ORIGINAL PREFACE 

IT IS now nearly thirty years since "A Manual for the Study of 
Insects," in the preparation of which I was aided by Mrs. Com- 

stock, was published. The great advances in the science of ento- 
mology during this period have made a revision of that work desirable. 
In the revision of the "Manual " so many changes and additions have 
been found necessary that the result is a book differing greatly from 
the original work; for this reason, it is published under a different 
title. The title selected is that of an earlier work, an "Introduction 
to Entomology" published in 1888 and long out of print. 

Part I of the present volume was published separately in 1919, in 
order that it might be available for the use of classes in insect mor- 
phology and also that an opportunity might be offered for the sugges- 
tion of desirable changes to be made before the incorporation of it in 
the completed work. Such suggestions have been received, with the 
result that some very important changes have been made in the text. 

In the preparation of this work I have received much help from 
my colleagues in the entomological department of Cornell University, 
for which I wish to make grateful acknowledgment, and especially 
to Dr. J. G. Needham for aid in the study of wing- venation, to Dr. 
O. A. Johannsen for help in the preparation of the chapter on the 
Diptera, to Dr. W. T. M. Forbes for help in the preparation of the 
chapter on the Lepidoptera, to Dr. J. C. Bradley for help in the prep- 
aration of the chapter on the Hymenoptera, and to Dr. J. T. Lloyd 
for the use of his figures of the cases of caddice worms. 

From the published works of Professors Herrick, Crosby and 
Slingerland, Crosby and Leonard, Sanderson, and Matheson I have 
gleaned much information; references to these and to the more im- 
portant of the other sources from which material has been drawn are 
indicated in the text and in the bibliography at the end of the volume. 



PRE FA CE 

References to the bibliography are made in the text by citing the 
name of the author and the year in which the paper quoted was 
pubHshed. 

The wood cuts used in the text were engraved from nature by 
Mrs. Anna B. Comstock for our joint work, "A Manual for the Study 
of Insects." The other original figures and the copies of published 
figures were drawn by Miss Anna C. Stryke, Miss Ellen Edmonson, 
Miss Mary Mekeel, Mr. Albert Force, Mrs. Louise Nash, and Miss 
E. L. Keyes. I am deeply indebted to each of these artists for the 
painstaking care shown in their work. 

As an aid to the pronunciation of the technical terms used and 
of the Latin names of insects, the accented syllable is marked with a 
sign indicating the quality of the vowel according to the English sys- 
tem of pronouncing Latin. 

Two objects have been kept constantly in mind in the preparation 
of this book: first, to aid the student in laying a firm foundation for 
his entomological studies; and second, to make available, so far as 
possible in the limited space of a handbook, a knowledge of the varied 
phenomena of the insect world. It is hoped that those who use this 
book will find delight in acquiring a more intimate acquaintance with 
these phenomena. 

John Henry Comstock 
Entomological Department 

Cornell University 
August IQ24. 



TABLE OF CONTENTS 

PART I. THE STRUCTURE AND METAMORPHOSIS 
OF INSECTS 



CHAPTER I 

Pages 

The Characteristics of Insects and Their Near Relatives i 

Phylum Arthropoda i 

List of the classes of the Arthropoda 2 

Table of the classes of the Arthropoda 3 

Class Onychophora 4 

Class Crustacea 6 

Class Palaeostracha 8 

Class Arachnida 9 

Class Pycnogonida 10 

Class Tardigrada 12 

Class Pentastomida 14 

Class Diplopoda 15 

Class Pauropoda 14 

Class Chilopoda 28 

Class Symphyla 23 

Class Myrientomata 24 

Class Hexapoda 26 



CHAPTER II 
The External Anatomy of Insects 29 



I. the structure of the body-wall 

a. The three layers of the body-wall 29 

The hypodermis 29 

The trichogens 3° 

The cuticula 3" 

Chitin 30 

Chitinized and non-chitinized cuticula 30 

The epidermis and the dermis 3^ 

The basement membrane 3 1 

b. The external apophyses of the cuticula 31 

The cuticular nodules 3^ 

The fixed hairs 3i 

The spines 32 

c. The appendages of the cuticula 32 

The spurs 32 



64455 



TABLE OF CONTENTS 

The setce 32 

The taxonomic value of setae 33 

A classification of setae 33 

(i) The clothing hairs 33 

(2) The glandular hairs 33 

(3) The sense-hairs 33 

The segmentation of the body 34 

The body-segments, somites or metamcrcs 34 

The transverse conjunctivae 34 

The segmentation of the appendages 34 

The divisions of a body-segment 34 

The tergum, the pleura, and the sternum 34 

The lateral conjunctivae 35 

The sclerites 35 

The sutures 35 

The median sutures 35 

The piliferous tubercles of larvae 35 

The homologizing of sclerites 35 

The regions of the body > 36 



2. THE HEAD 

The corneas of the eyes 36 

The corneas of the compound eyes 36 

The corneas of the ocelli 37 

The areas of the surface of the head 37 

The front 37 

The clypeus 38 

The labrum 38 

The epicranium 38 

The vertex 39 

The occiput 39 

The genag 39 

The postgenas 39 

The gula 39 

The ocular sclerites 39 

The antennal sclerites 39 

The trochantin of the mandible 40 

The maxillary pleurites 40 

The cervical sclerites 40 

The appendages of the hsad 40 

The antennas 40 

The mouth-parts 42 

The labrum 42 

The mandibles 42 

The maxillulae 42 

The maxillae 42 

The labium or second maxillas 45 



TABLE OF CONTENTS xi 

The epipharynx 46 

The hypopharynx 47 

d. The segments of the head 47 

3. THE THORAX 

c. The segments of the thorax 48 

The prothorax, mesothorax, and metathorax 48 

The alitrunk 49 

The propodeum or the median segment 49 

b. The sclerites of a thoracic segment 49 

The sclerites of a tergum 49 

The notum 49 

The postnotum or the postscutellum 50 

The divisions of the notum 50 

The patagia 50 

The parapsides 51 

The sclerites of the pleura 51 

The episternum 51 

The epimerum 51 

The preepistemum 51 

The paraptera , 51 

The spiracles 52 

The peritremes 52 

The acetabula 52 

The sclerites of a sternum 52 

c. The articular sclerites of the appendages 53 

The articular sclerites of the legs 53 

The trochantin 53 

The antecoxal piece 54 

The second antecoxal piece 54 

The articular sclerites of the wings 54 

The tegula 54 

The axillaries 54 

d. The appendages of the thorax 55 

The legs 56 

The coxa 56 

The styli 56 

The trochanter 57 

The f emiu: 57 

The tibia 57 

The tarsus 57 

The wings 58 

The different types of wings 59 

The margins of wings 60 

The angles of wings 60 

The axillary cord 60 

The axillary membrane 60 

The alula 60 

The axillary excision 61 



TABLE OF CONTENTS 

The posterior lobe 6i 

The methods of uniting the two wings of each side 6i 

The hamuli 6i 

The frenulum and the frenulum hook 6i 

The jugum 6i 

The fibula 62 

The hypothetical type of the primitive wing-venation 62 

Longitudinal veins and cross-veins 64 

The principal wing-veins 64 

The chief branches of the wing-veins 64 

The veins of the anal area 65 

The reduction of the number of the wing-veins 65 

Serial veins 67 

The increase of the number of the wing- veins 68 

The accessory veins 68 

The intercalary veins 69 

The adventitious veins 7° 

The anastomosis of veins 70 

The named cross-veins 71 

The arculus 72 

The terminology of the cells of the wing 72 

The corrugations of the wings 73 

Convex and concave veins 73 

The furrows of the wing 73 

The bullae 74 

The ambient vein 74 

The humeral veins 74 

The pterostigma or stigma 74 

The epiplurae 74 

The discal cell and the discal vein 74 

The anal area and the preanal area of the wing 75 



4. THE ABDOMEN 75 

a. The segments of the abdomen 75 

b. The appendages of the abdomen 7^ 

The styli or vestigial legs of certain Thysanura 76 

The coUophore of the Collembola 7^ 

The spring of the Collembola 7^ 

The genitalia 7^ 

The cerci 77 

The median caudal filament 7^ 

The prolegs of larvae 7^ 



5. THE MUSIC AND THE MUSICAL ORGANS Cr INSECTS 78 

a. Sounds produced by striking objects outside of the body 79 

b. The music of flight 80 



TABLE OF CONTENTS xiii 

c. Stridulating organs of the rasping type 8i 

The stridulating organs of the Locustidse 82 

The stridulating organs of the Gryllidae and the Tettigoniidag 83 

Rasping organs of other than orthopterous insects 87 

d. The musical organs of a cicada 89 

e. The spiracular musical organs 91 

/. The acute buzzing of flies and bees 91 

g. Musical notation of the songs of insects 92 

h. Insect choruses 93 

CHAPTER III 

The Internal Anatomy of Insects 94 

i. the hypodermal structures 95 

a. The internal skeleton 95 

Sources of the internal skeleton 95 

Chitinized tendons 95 

Invaginations of the body-wall or apodemes 95 

The tentorium 96 

The posterior arms of the tentorium 96 

The anterior arms of the tentorium 97 

The dorsal arms of the tentorium 97 

The frontal plate of the tentoritun 97 

The endothorax 97 

The pragmas 97 

The lateral apodemes 98 

The furcae 98 

b. The hypodermal glands 98 

The molting-fluid glands 99 

Glands connected with setae 99 

Venomous setae and spines 100 

Androconia 100 

The specific scent-glands of females 100 

Tenent hairs 100 

The osmeteria loi 

Glands opening on the surface of the body 102 

Wax-glands 102 

Froth-glands of spittle insects 102 

Stink -glands 102 

The cephalic silk-glands 103 

The salivary glands 104 

2. THE MUSCLES IO4 

3. THE ALIMENTARY CANAL AND ITS APPENDAGES IO7 

a. The more general features 107 

The principal divisions 108 

Imperforate intestines in the larvae of certain insects 108 



TABLE OF CONTENTS 

b. The fore-intestine 109 

The layers of the fore-intestine 109 

The intima 109 

The epithelium 109 

The basement membrane 109 

The longitudinal muscles 109 

The circular muscles 109 

The peritoneal membrane 109 

The regions of the fore-intestine 109 

The pharynx 109 

The oesophagus 1 10 

The crop no 

The proventriculus no 

The oesophageal valve in 

c. The mid-intestine Ill 

The layers of the mid-intestine in 

The epithelium 112 

The peritrophic membrane 112 

d. The hind-intestine 112 

The layers of the hind-intestine 112 

The regions of the hind-intestine 113 

The Malpighian vessels 113 

The Malpighian vessels as silk-glands 113 

The caecum 113 

The anus 113 

4. THE RESPIRATORY SYSTEM II3 

a. The open or holopneustic type of respiratory organs 114 

1. The spiracles 114 

The position of the spiracles 114 

The number of spiracles 114 

Terms indicating the distribution of the spiracles 115 

The structure of spiracles 116 

The closing apparatus of the tracheae 116 

2. The trachece 116 

The structure of the trachea 117 

3. The tracheoles 118 

4. The air-sacs 118 

5. Modifications of the open type of respiratory organs 119 

b. The closed or apneustic type of respiratory organs • 119 

/. The Tracheal gills 119 

2. Respiration of parasites 120 

3. The blood-gills 120 



TABLE OF CONTENTS XV 

5. THE CIRCULATORY SYSTEM 121 

The general features of the circulatory system 12 1 

The heart 121 

The pulsations of the heart 122 

The aorta 122 

The circulation of the blood 122 

Accessory circulatory organs 122 

6. THE BLOOD 122 

7. THE ADIPOSE TISSUE I23 

8. THE NERVOUS SYSTEM 123 

The central nervous system 123 

The oesophageal sympathetic nervous system 125 

The ventral sympathetic nervous system 127 

The peripheral sensory nervous system 128 

9. GENERALIZATIONS REGARDING THE SENSE-ORGANS OF INSECTS.. . 1 29 

A classification of the sense-organs 129 

The cuticular part of the sense-organs 130 

10. THE ORGANS OF TOUCH I3I 

11. THE ORGANS OF TASTE AND SMELL I32 

12. THE ORGANS OF SIGHT 134 

The general features I34 

The two types of eyes I34 

The distinction between ocelli and compound eyes 134 

The absence of compound eyes in most of the Apterygota 135 

The absence of compound eyes in larvae I35 

The ocelH I35 

The primary ocelli i35 

The adaptive ocelli 136 

The structure of a visual cell I37 

The structure of a primary ocellus I37 

Ocelli of Ephemerida i39 

The compound eyes I39 

The physiology of compound eyes 141 

The theory of mosaic vision 14^ 

Day-eyes 14^ 

Night-eyes H3 

Eyes with double function i43 

Divided eyes H4 

The tapetum ^44 



TABLE OF CONTENTS 

13. THE ORGANS OF HEARING 145 

The general featiires 145 

The tympana 145 

The chordotonal organs 145 

The scolopale and the scolopophore 146 

The integumental and the subintegumental scolopophores 146 

The structure of a scolopophore 146 

The structure of a scolopale 147 

The simpler forms of chordotonal organs 147 

The chordotonal ligament 147 

The chordotonal organs of larvse 148 

The chordotonal organs of the Locustidae 148 

The chordotonal organs of the Tettigoniidae and of the Gryllida;. . . 149 

The trachea of the leg 1 50 

The spaces of the leg 151 

The supra-tympanal or subgenual organ 151 

The intermediate organ 152 

Siebold's organ or the crista acustica 152 

Johnston's organ 1 52 



14. SENSE-ORGANS OF UNKNOWN FUNCTIONS 

The sense-domes or the olfactory pores 154 

15. THE REPRODUCTIVE ORGANS 

The general features 156 

Secondary sexual characters 157 

The reproductive organs of the female 157 

The general features of the ovary 157 

The wall of an ovarian tube 158 

The zones of an ovarian tube 158 

The contents of an ovarian tube 158 

The egg-follicles 158 

The functions of the follicular epithelium 159 

The ligament of the ovary 1 59 

The oviduct 1 59 

The egg-calyx 1 59 

The vagina 1 59 

The spsrmatheca 159 

The bursa copulatrix 1 59 

The colleterial glands 160 

The reproductive organs of the male 160 

The general features of the testes 160 

The structure of a testicular follicle 161 

The spermatophores 1 62 

Otlier structures 162 



TABLE OF CONTENTS xvii 

l6. THE SUSPENSORIA OF THE VISCERA 

The dorsal diaphragm 1 62 

The ventral diaphragm 165 

The thread-like suspensoria of the viscera 163 

17. SUPPLEMENTARY DEFINITIONS 

The oenocytes 163 

The pericardial cells 164 

The phagocytic organs 164 

The light-organs 165 

CHAPTER IV 

The Metamorphosis of Insects 166 

I. the EXTERNAL CHARACTERISTICS OF THE METAMORPHOSIS OF INSECTS 

a. The egg 1 66 

The shape of the egg 167 

The sculpture of the shell 167 

The microphyle 167 

The number of eggs produced by insects 168 

Modes of laying eggs 168 

Duration of the egg-state 170 

b. The hatching of young insects 171 

The hatching spines 171 

c. The molting of insects 171 

General features of the molting of insects 171 

The molting fluid 172 

The number of postembryonic molts 172 

Stadia 172 

Instars 172 

Head measurements of larva; 173 

The reproduction of lost limbs 173 

d. Development without metamorphosis 174 

The Ametabola 174 

e. Gradual metamorphosis 175 

The Paurometabola 176 

The term nymph 176 

Deviations from the usual type 176 

The Saltitorial Orthoptera 177 

The Cicadas 177 

The Coccidae 177 

The Aleyrodida; 177 

The Aphididse 177 

The Thysanoptera . 177 

/. Incomplete metamorphosis 178 

The Hemimetabola 179 

The term naiad 179 

Deviations from the usual type 1 80 

The Odonata 180, 

The Ephemerida ,,.,,... 180 



i TABLE OF CONTENTS 

g. Complete metamorphosis l8o 

The Holometabola i8o 

The term larva l8o 

The adaptive characteristics of larvae i8i 

The different types of larvae 183 

The prepupa 185 

The pupa 186 

The chrysalis 186 

Active pupae 187 

The cremaster 187 

The cocoon 188 

Modes of escape from the cocoon 188 

The puparium 190 

Modes of escape from the puparium 190 

The different types of pupae 190 

The imago 191 

h. Hypermetamorphosis 191 

i. Viviparous insects 191 

Viviparity with parthenogenetic reproduction 192 

Viviparity with sexual reproduction 193 

j. Neoteinia 194 

2. THE DEVELOPMENT OF APPENDAGES I94 

a. The development of wings 195 

The development of the wings of nymphs and naiads 195 

The development of the wings in insects with a complete meta- 
morphosis 195 

b. The development of legs 197 

The development of the legs of nymphs and naiads 198 

The development of the legs in insects with a complete meta- 
morphosis 198 

c. The development of antennae 199 

d. The development of mouth-parts 200 

e. The development of the genital appendages 201 

3. THE DEVELOPMENT OF THE HEAD IN THE MUSCID^ 202 

4. THE TRANSFORMATION OF THE INTERNAL ORGANS 204 



TABLE OF CONTENTS 



PART II. THE CLASSIFICATION AND THE 
LIFE-HISTORIES OF INSECTS 

Chapter V. — The sub-classes and the orders of the class Hexapoda . . 206 

Chapter VI. — Class Hexapoda 217 

Chapter VII.— The Apterygota 218 

Chapter VII. —Order Protura 218 

Chapter VII. — Order Thysanura 219 

Chapter VII. — Order Collembola 225 

Chapter VIIL— The Pterygota 

Chapter VIIL — Order Orthoptera 230 

Chapter IX. — Order Zoraptera 270 

Chapter X. — Order Isoptera 273 

Chapter XL — Order Neuroptera 281 

Chapter XII. — Order Ephemerida 308 

Chapter XIIL — Order Odonata 314 

Chapter XIV. — Order Plecoptera , 325 

Chapter XV. — Order Corrodentia 331 

Chapter XVI. — Order Mallophaga 335 

Chapter XVII. —Order Embiidina 338 

Chapter XVIII. — Order Thysanoptera 341 

Chapter XIX. — Order Anoplura 347 

Chapter XX. — Order Hemiptera 350 

Chapter XXI. — Order Homoptera 394 

Chapter XXII. — Order Dermaptera 460 

Chapter XXIII. — Order Coleoptera 464 

Chapter XXIV. — Order Strepsiptera 546 

Chapter XXV. — Order Mecoptera 550 

Chapter XXVL -Order Trichoptera 555 

Chapter XXVIL — Order Lepidoptera 571 

Chapter XXVIIL —Order Diptera 773 

Chapter XXIX. — Order Siphonaptera 877 

Chapter XXX. — Order Hymenoptera 884 

Bibliography 1008 

Index 1029 



PART I 

THE STRUCTURE AND METAMORPHOSIS 
OF INSECTS 



CHAPTER I 

THE CHARACTERISTICS OF INSECTS AND OF THEIR 
NEAR RELATIVES 



Phylum ARTHROPODA 
The Arthr 



If an insect, a scorpion, a centipede, or a lobster be examined, 
the body will be found to be composed of a series of more or less 
similar rings or segments joined together; and some of these seg- 
ments will be found to bear jointed legs (Fig. i) . All animals possess- 
ing these characteristics are classed together 
as the Arthr opoda, one of the chief divisions or 
phyla of the animal kingdom. 

A similar segmented form of body is found 
among worms; but these are distinguished 
from the Arthropoda by the absence of legs. 
It should be remembered that many animals 
commonly called worms, as the tomato-worm, 
the cabbage-worm, and others, are not true 
worms, but are the larvae of insects (Fig. 2). 
The angle-worm is the most familiar example 
of a true worm. 

In the case of certain arthropods the dis- 
tinctive characteristics of the phylum are 
not evident from a ciu-sory examination. 
This may be due to a very generalized condi- 
tion, as perhaps is true of Peripatus; but in 
Fig. I. — An arthropod, most instances it is due to a secondary modifi- 
cation of form, the result of adaptation to 
special modes of life. Thus the segmentation of the body may be 





Fig. 2. — ^A larva of an insect. 
(1) 



.v^^^<^ 




AN INTRODUCTION TO ENTOMOLOGY 



many other insects. 




obscured, as in spiders and in mites (Fig. 3) ; or the jointed append- 
ages may be absent, as in the larvae of flies (Fig. 4), of bees, and of 
In all of these cases, however, a careful study 
of the structure of the animal, or 
of its complete life-history, or of 
other animals that are evidently 
closely allied to it removes any 
doubt regarding its being an 
arthropod. 

The phylum Arthropoda is 

the largest of the phyla of the 

animal kingdom, including many 

more known species than all the 

other phyla taken together. This 

Fig. 3.— A mite, an arth- vast assemblage of animals in- 

ropod in which the ^^^^^g f^^^g differing widely in 

segmentation or the " -^ 

body is obscured. The structure, all agreemg, however, 

in the possession of the essential 
characteristics of the Arthropoda. 
Several distinct types of arthropods are recognized; 
and those of each type are grouped together as a class. 
The number of distinct classes that should be recog- 
nized, and the relation of these classes to each other are 
matters regarding which there are still differences of 
opinion ; we must have much more knowledge than we 
now possess before we can speak with any degree of 
certainty regarding them. 

Each of the classes enumerated below is regarded by 
all as a distinct group of animals ; but in some cases there 
may be a question whether the group should be given 
the rank of a distinct class or not. The order in which the classes 
are discussed in this chapter is indicated in the following list. 



southern cattle-tick, 
Boophilus annulatus. 




LIST OF THE CLASSES OF THE ARTHROPODA 
THE MOST PRIMITIVE ARTHROPODS 

Class Onychophora, page 4 

THE AQUATIC SERIES 

Class Crustacea, page 6 
Class Palaeostracha, page 8 

AN OFFSHOOT OF THE AQUATIC SERIES, SECONDARILY AERIAL 

Class Arachnida, page 9 



CHARA CTERISTICS OF INSECTS AND THEIR RELA TIVES 3 

IV. DEGENERATE ARTHROPODS OF DOUBTFUL POSITION 

Class Pycnogonida, page lo 
Class Tardigrada, page 12 
Class Pentastomida, page 14 

V. THE PRIMARILY AERIAL SERIES 

Class Onychophora (See above) 
Class Diplopoda, page 15 
Class Pauropoda, page 18 
Class Chilopoda, page 20 
Class Symphyla, page 23 
Class Myrientomata, page 24 
Class Hexapoda, page 26 

TABLE OF CLASSES OF THE ARTHROPODA 

A. Worm-like animals, with an unsegmented body, but with many 

unjointed legs Onychophora 

AA. Body more or less distinctly segmented except in a few degen- 
erate forms. 
B. With two pairs of antennae and at least five pairs of legs; 

respiration aquatic Crustacea 

BB. Without or apparently without antenucE. 

C. With well-developed aquatic respiratory organs. 

PaL/EOSTRACHA 

CC. With well-developed aerial respiratory organs or with- 
out distinct respiratory organs. 
D. With well-developed aerial respiratory organs. 

E. Body not resembhng that of the Thysanura in form. 

Arachnida 
EE. Body resembling that of the Thysanura in form 

(Family Eosentomidas) Myrientomata 

DD. Without distinct respiratory organs. 
E. With di"tinctly segmented legs. 
F. Body resembling that of the Thysanura in form, but 
without antennas, and with three pairs of thoracic 
legs and three pairs of vestigial abdominal legs 

(Family Acerentomidcs) Myrientomata 

FF. With four or five pairs of ambulatory legs; 

abdomen vestigial Pycnogonida 

EE. Legs not distinctly segmented. 

F. With four pairs of legs in the adult instar. 

Tardigrada 



AN INTRODUCTION TO ENTOMOLOGY 

FF. Larva with two pairs of legs, adult without 

legs Pentastomida 

BBB. With one pair, and only one, of feeler-like antennae. 
Respiration aerial. 
C. With more than three pairs of legs, and without wings. 
D, With two pairs of legs on some of the body-segments. 

DiPLOPODA 

DD . With only one pair of legs on each segment of the body. 

E. Antennas branched Pauropoda 

EE. Antennae not branched. 

F. Head without a Y-shaped epicranial suture. 
Tarsi of legs with a single claw each. Opening of 
the reproductive organs near the caudal end of 

the body Chilopoda 

FF. Head with a Y-shaped epicranial suture, as in 
insects. Tarsi of legs with two claws each. 
Opening of the reproductive organs near the head. 

Symphyla 

CC. With only three pairs of legs, and usually with wings in 
the adult state Hexapoda 



Class ONYCHOPHORA 

The genus Peripatus of authors 
The members of this class are air-breathing animals, with a nearly 
cylindrical, unsegmented body, which is furnished with many pairs of 
unjo-'ntcd legs. The reproductive organs open near thehindend ofthebody. 
The class Onychophora occupies the position of a connecting link 
between the Arthropoda and the phylum Annulata or worms; and is 
therefore of the highest interest to students of systematic zoology. 
All known members of this class have been included until recently in a 
single genus Pertpatus; but now the fifty or more known species are 
distributed among nearly a dozen genera. 

The body 
(Fig. 5) is nearly 
cylindrical, cat- 
erpillar - like in 
form, but is un- 
segmented ex- 
ternally. It is 
I^ig. 5- — Peripatoides novcB-zealandicce. furnished with 

many pairs of legs, the number of which varies in different species. 
The legs have a ringed appearance, but are not distinctly jointed. 





CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 5 

The head bears a pair of ringed antennae (Fi^. 6) ; behind these on 
the sides of the head, there is a pair of short appendages termed oral 
papillae. The mouth opening is surrounded by a row of lobes which 
constitute the lips, and between these in the anterior part of the 
mouth-cavity there is an obtuse pro- 
jection, which bears a row of chitinous 
points. Within the mouth cavity there 
are two pairs of hooked plates, which 
have been termed the mandibles, the 
two plates of each side being regarded 
a? a single mandible. 

Although the body is unsegmented 
externally, internally there are evi- 
dences of a metameric arrangement of 
parts. The ventral nerve cords, which 
at first sight appear to be without ^r/ 
ganglia, are enlarged opposite each 
pair of legs, and these enlargments 
are regarded as rudimentary ganglia. Fig. 6.-Ventral view of the head 
We can, therefore speak of each sec- and first pair of legs of Peri- 
,• i: u J J- 4. paloides; a, antenna; o, oral 

tion of a body corresponding to a papilla. 

pair of appendages as a segment. The 

metameric condition is farther indicated by the fact that most of 
these segments contain each a pair of nephridia; each nephridium 
opening at the base of a leg. 

The respiratory organs are short tracheae, which are rareiy 
branched, and in which the t^nidia appear to be rudimentary.* In 
some species, the spiracles are distributed irregularly; in others, they 
are in longitudinal rows. 

The sexes are distinct. The reproductive organs open near the 
hind end of the body, either between the last or the next to the last 
pair of legs. 

The various species are found in damp situations, under the bark 
of rotten stumps, under stones or other objects on the ground. They 
have been found in Africa, in Australia, in South America, and in the 
West Indies. 

Their relationship to the Arthropoda is shown by the presence of 
paired appendages, one, or perhaps two, pairs of which are modified as 
jaws; the presence of tracheae which are found nowhere else except 

*It is quite possible that the "short trachese" described by writers on the 
structure of these animals are tracheoles. See the account of the distinguishing 
features of tracheae and tracheoles m Chapter III. 



6 



AN INTRODUCTION TO ENTOMOLOGY 



in the Arthropoda; the presence of paired ostia in the wall of the 
heart ; and the presence of a vascular body cavity and pericardium. 

They resemble the Annulata in having a pair of nephridia in most 
of the segments of the body corresponding to the pairs of legs, and in 
having ciha in the generative tracts. 

An extended monograph of the Onychophora v/as published by 
Bouvier ('05-07). 

Class CRUSTACEA 
The Crustaceans 

The members of this class are 
aquatic arthropods, which breathe 
by true gills. They have two 
pairs of antennce and at least five 
pairs of legs. The position of the 
openings of the reproductive organs 
varies greatly; hut as a rule they 
are situated far forward. 

The most familiar examples 
of the Crustacea are the cray- 
fishes, the lobsters, the shrimps, 
and the crabs, Cray-fishes (Fig. 
7) abound in our brooks, and are 
often improperly called crabs. 
The lobsters, the shrimps, and 
the true crabs live in salt 
water. 
Excepting Llmulus, the sole living representative of the class 
described next, the Crus- 
tacea are distinguished 
from all other arthro- 
pods by their mode of 
respiration, being the 
only ones that breathe 
by true gills. Many in- 
sects live in water and 
are furnished with gill- 
like organs; but these 
are either tracheal gills or 
blood-gills, organs which 
differ essentially in struc- 
ture from true gills, as Cypndopsis, c, Cyclops. 




A cray-iish. 




Daphnia; 



CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 



described later. The Crustacea also differ from other Arthropoda 
in having two pairs of antennae. Rudiments of two pairs of antennae 
have been observed in the embryos of many other arthropods ; but 
in these cases one or the other of the two pairs of antennas fail 
to develop. 

The examples of crustaceans named above are the more con- 
spicuous members of the class; but many other smaller forms abound 
both in the sea and in fresh water. Some of the more minute fresh- 
water forms are almost sure to occur in any fresh-water aquarium. 

In Figure 8 are repre- 
sented three of these 
greatly enlarged. The 
minute crustaceans form 
an important element in 
the food of fishes. 

Some crustaceans live 
in damp places on land, 
and are often found by 
c(;llectors of insects; 
those most often ob- 
served are the sow-bugs 
(Oniscoida), which fre- 
quently occur about 
water-soaked wood. 
Figure 9 represents one 
of these. 
As there are several, most excellent text books devoted to the 
Crustacea, it is unnecessary to discuss farther this class in this place. 




Fig. 9. — A sow -bug, Cylisticus convexus (From 
Richardson after Sars). 



AN INTRODUCTION TO ENTOMOLOGY 



Class PAL^OSTRACHA 

The King-crabs or Horseshoe-crabs 

The members of this class 
are aquatic arthropods, which 
resemble the Crustacea in that 
they breathe by true gills, but 
in other respects are closely 
allied to the Arachnida. They 
are apparently without 
antenna, the appendages hom- 
ologous to antenncB being not 
feeler-like. The reproductive 
organs open near the base of 
the abdomen. 

The class Palseostracha 
is composed almost entirely 
of extinct forms, there being 
living representatives of only 
a single order, the Xiphosura, 
and this order is nearly 
extinct; for of it there re- 
mains only the genu? 
Lhnulus, represented b / 
only five known species. 

The members of this 
genus are known as king- 
crabs or horseshoe-crabs ; 
the former name is sug- 
gested by the great size of some of the species; the latter, by 
shape of the cephalothorax (Fig. lo). 

The king-crabs are marine; they are found on our Atlantic Coast 
from Maine to Florida, in the West Indies, and on the eastern shores 
of Asia. They are found in from two to six fathoms of water on 
sandy and muddy shores; they burrow a short distance in the sand 
or mud and feed chiefly on worms. The single species of our coast is 
Ltmulus polyphemus. 




Fig. 10. — A horseshoe crab, Limulus (After 
Packard). 



the 



CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 3 

Class ARACHNIDA 
Scorpions, Harvestmen, Spiders, Mites, and others 

The members of this class are air-breathing arthropods, in which the 
head and thorax are usually grown to getlier, forming a cephalothorax, 
which have four pairs of legs, and which apparently have no antennce. 
The reproductive organs open near the base of the abdomen. 




Fig. II. — Arachnids: a, a scorpion; b, a harvestman. 
c, a spider; d, an itch-mite, from below and from 
above. 



The Arachnida abound wherever insects occur, and are often 
mistaken for insects. But they can be easily distinguished by the 
characters given above, even in those cases where an exception occurs 
to some one of them. The more important of the exceptions are the 
following: in one order, the Solpugida, the head is distinct from the 



10 AN INTRODUCTION TO ENTOMOLOGY 

thorax; as a rule the young of mites have only six legs, but a fourth 
pair is added during growth ; and in the gall-mites there are only four 
legs. 

The Arachnida are air-breathing; but it is believed that they 
have been evclved from aquatic progenitors. Two forms of respira- 
tory organs exist in this class : first, book-lungs ; and second, tubular 
trachea. Some members of it possess only one of these types • but 
the greater number of spiders possess both. 

A striking characteristic of the Arachnida, which, however, is also 
possessed by the Palaeostracha, is the absence of true jaws In other 
arthropods ore or more pairs of appcndag es a e jaw-like i form and 
are used exclusively as jaws ; but in the Arachnida the p- e^ is crushed 
either by the modified antennas alone or by these organs and other 
more or less leg-like appendages. The arachnids suck the blood of 
their victims by means of a sucking stomach; they crush their prey, 
but do not masticate it so as to swallow the solid parts. 

In the Arachnida there exist only simple eyes. 

The reproductive organs open near the base of the abdomen on the 
ventral side. In this respect the Arachnida resemble Limidus, the 
millipedes, and the Crustacea, and differ from the centipedes and 
insects. 

Among the more familiar representatives of this class are the 
scorpions (Fig. ii, a), the harvestmen (Fig. ii, b), the spiders (Fig. 
II, c), and the mites (Fig. ii, d). 

As the writer has devoted a separate volume (Comstock, '12) to 
the Arachnida, it will not be discussed farther in this place. 



Class PYCNOGONIDA 

The Pycnogonids 

The members of this class are marine arachnid-like arthropods, in 
•which the cephaloihorax bears typically seven pairs 0} jointed appen- 
dages, but in afewfcrms there are eight pairs, and in some the anterior 
two or three pairs are absent; and in which the abdomen is reduced to a 
legless, unsegmented condition. They possess a circulatory system, but 
no evident respiratory organs. The reproductive organs open through 
the second segment of the legs; the number of legs bearing these opening 
varies f rem one to five pairs. 

The Pycnogonida or pycnogonids are marine animals, which bear 
a superficial resemblance to spiders (Fig. 12). Some of them are 
f oimd under stones, near the low water line, on sea shores ; but they 



CHARA CTERISTICS OF INSECTS A ND THEIR RELA TIVES 1 1 

are more abundant in deep water. Some are found attached to sea- 
anemones, upon which they probably prey; others are found climbing 




Fig. 12. — A pycnogonid, Nymphon hispidiim: c, chelophore; p, 
palpus; o, ovigerous legs; /, /, I, I, ambulatory legs; ab, abdo- 
men (After Hoeck). 

over sea-weeds and Hydroids; and sometimes they are dredged in 
great numbers from deep water. 

They possess a suctorial proboscis. In none of the appendages are 
the basal segments modified into organs for crushing the prey. 

The cephalothorax comprises almost tl e entire body ; the abdomen 
being reduced to a mere vestige, without appendages, and with no 
external indication of segmentation. But the presence of two pairs 
of abdominal ganglia indicates that originally the abdomen consisted 
of more than one segment. 

There are typically seven pairs of appendages; but a few forms 
possess eight pairs ; and in some the first two or three pairs are absent. 
The appendages, when all are present, consist of a pair of chelophores, 
each of which when well-developed consists of one or two basal seg- 
ments and a chelate "hand"; the palpi, which are supposed to be 
tactile, and which have from five to ten joints when well-developed; 
the ovigerous legs, which are so-called because in the males they are 
used for holding the mass of eggs beneath the body; and the ambula- 
tory legs, of which there are usually four pairs, but a few forms possess 
a fifth pair. The ambulatory legs consist each of eight segments and 
a terminal claw. 

The only organs of special sense that have been found in these 
animals are the eyes. These are absent or at least very poorly 



12 ^A^ INTRODUCTION TO ENTOMOLOGY 

developed in some forms, especially those that are found in very deep 
water, i.e. below four or five hundred fathoms. When well-developed 
they are simple, and consist of two pairs, situated on a tubercle, on 
the head or the first compound segment of the body, the segment that 
bears the first four pairs of appendages. 

The reproductive organs open in the second segment of the legs. 
In some these openings occur only in the last pair of legs; in others, in 
all of the ambulatory legs. 

Very little is known regarding the habits of these animals. The 
most interesting features that have been observed are perhaps the 
facts that the males carry the eggs in a mass, held beneath the body 
by the third pair of appendages, the ovigerous legs, and also carry 
the young for a time. 

As to the systematic position of the class Pycnogonida, very little 
can be said. These animals are doubtless arthropods, and they are 
commonly placed near the Arachnida. 

Class TARDIGRADA 

The Tardigrades or Bear Animalcules 

The members of this class are very minute segmented animals, with 
four pairs of legs, hut without antenna; or mouth-appendages, and without 
special circulatory or respiratory organs; the reproductive organs open 
into the intestine. 

The Tardigrada or tardigrades are microscopic animals, measuring 
from one seventy-fifth to one twenty-fifth of an inch in length. They 
are somewhat mite-like in appearance; but are very different from 
mites in structure (Fig. 13 and 14). 

The head bears neither antennae nor mouth-appendages. The 
four pairs of legs are short, unjointed, and are distributed along the 

entire length of the body, the 
fourth pair being at the cau- 
dal end. Each leg is termin- 
ated by claws, which differ in 
number and form in different 
genera. 

The more striking features 
of the internal structure of 
Fig. 13.-A tardigrade (After Doyere). these animals is the absence of 

special circulatory and respiratory organs; the presence of a pair of 
chitinous teeth, either in the oral cavity or a short distance back of 




CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 13 



it ; the presence of Malpighian tubules ; the unpaired condition of 
the reproductive organs of both sexes; and the fact that these organs 
open into the intestine. The central nervous system consists of a 
brain, a suboesophageal ganghon, and a ventral chain of four ganglia, 
connected by widely separated connectives. 

The tardigrades are very abundant, and are very widely dis- 
tributed. Some live in fresh water, a few are marine, but most of 
them live in damp places, and especially on the roots of moss, growing 
in gutters, on roofs or trees, or in ditches. 
But although they are common, their 
minute size and retiring habits result in 
their being rarely seen except by those 
who are seeking them. 

Many of them have the power of 
withstanding desiccation for a long period. 
This has been demonstrated artificially by 
placing them on a microscopic slide and 
allowing the mositure to evaporate 
slowly. The body shrinks, its skin 
becomes wrinkled, and finally it assumes 
the appearance of a grain of sand in 
which no parts can be distinguished. In 
this state they can remain, it is said, for 
years; after which, if water be added, 
the body swells, assumes its normal form, 
and after a time, the creatures resume 
their activities. 

Regarding the systematic position of 
this class of animals nothing definite can 

be stated beyond the fact that they are doubtless arthropods. Their 
relationship to the other classes of arthropods has been masked by 
degenerative modifications. They are placed here near the end of 
the series of classes of arthropods, merely as a matter of convenience, 
in what may be termed an appendix to the arthropod series, which 
includes animals of doubtful relationships. 




Fig. 14. — A tardigrade (After 
Doyere). 



14 



AN INTRODUCTION TO ENTOMOLOGY 



Class PENTASTOMIDA 
The Pentastomids or Linguatulids 
The members of this class are degenerate, worm-like, parasitic 
q/fthropods , which in the adidt state have no appendages, except two pairs 
of hooks near the mouth; the larvce have two pairs of short legs. These 
animals possess neither circidatory nor respiratory organs. The 
reproductive organs of t!ie male open a short distance behind the mouth; 
those of the female near the caudal end of the body. 

The Pentastomida or pentastomids are worm-like creatures, whose 
form has been greatly modified by their parasitic life. The adults 
bear little resemblance to any other arthropods. Representatives of 
three genera are known. These are Lingudtula in which the body is 
fluke-like in form(Fig. 15) and superficially annulated; Porocephalus, 
in which the body is cylindrical (Fig. 16) and ringed; and Re igJidrdia, 
which is devoid of annulations, and with poorly developed hooks and 
a mouth-armature. 

The arthropodan nature of these animals is 
indicated by the form of the larvae, which although 
greatly degenerate, are less so than the adults, 
having two pairs of legs (Fig. 17). 




Fig. 15. — A pertasto- 
mid, I.ini^ uattila 
t a ni oilers, f irnle at 
the time of copula- 
tion: //, hooks; oe, 
cesopliaur.s, rs. re- 
ceptanila seniini?, 
one of which is still 
empty; i, ir.testine; 
07', ovary; fa, vagina 
(From Lang after 
Leuckart), 




Fig. 1 6. — A pentastomid, 
Porocephalus annulaius; 
a, ventral view of head, 
greatly enlarged; b, 
ventral view of animal, 
slighlly enlarged (After 
Shipley). 



Fig. 17 — A pentastomid, larva of 
Poroi fpJialus proboscidens, seen 
from below, highly magnified: I, 
boring anterior end; 2, first pair 
of chitinons processes seen be- 
tween the fo'ks of the second pair; 
3, ventral nerve ganglion; 4, ali- 
mentary canal, 5, mouth; 6 anc 
7, gland cells (From Shipley after 
Stiles). 



CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 15 

Like many of the parasitic worms, these animals, in soma cases at 
least, pass their larval life in one host, and complete their development 
in another of a different species ; some larvae being found in the bodies 
of herbivorous animals and the adults in predacious animals that feed 
on these herbivorous hosts. 

The systematic position of the pentastomids is very uncertain. 
They have been considered by some writers to be allied to the mites. 
But it seems better to merely place them in this appendix to the 
arthropod series until more is known of their relationships. 



Class DIPLOPODA 
The Millipedes or Diplopods 

The members of this class are air-breathing arthropods in which the 
head is distinct, and the remaining segments of the body form a continuous 
region. The greater number of the body-segments are so grouped that 
each apparent segment bears two pairs of legs. The antennce are short 
and very similar to the legs. The openings of the reproductive organs are 
paired, and situated behind the second pair of legs. 



i^'ig. 1 8. — A millipede, Spiroholus marginatus. 

The Diplopoda and the three following classes were formerly 
grouped together as a single class, the Myridpoda. But this grouping 
has been abandoned, because it has been found that the Chilopoda are 
more closely allied to the insects than they are to the DiplopDda; and 
the Pauropoda and Symphyla are both very distinct from the Diplo- 
poda on the one hand and the Chilopoda on the other. Owing to the 
very general and long continued use of the term Myriapoda, the 
student who wishes to look up the literature on these four classes 
should consult the references under this older name. 

The most distinctive feature of the millipedes is that which sug- 
gested the name Diplopoda for the class, the fact that throughout the 
greater part of the length of the body there appears to be two pairs of 
legs borne by each segment (Fig. i8). 

This apparent doubling of the appendages is due to a grouping of 
the segments in pairs and either a consolidation of the two terga of 



16 



AN INTRODUCTION TO ENTOMOLOGY 



each pair or the non-development of one of them; which of these 
alternatives is the case has not been definitely determined. 

It is clear, however, that there has been a grouping of the seg- 
ments in pairs in the region where the appendages are doubled, for 
corresponding with each tergum there are two sterna and two pairs of 
spiracles. 

A few of the anterior body segments, usually three or four in 
number, and sometimes one or two of the caudal segments remain 
single. Frequently one of the anterior single segments is legless, but 
the particular segment that lacks legs differs in the different families. 

The head, which is as distinct as is the head of insects, bears the 

antennae, the eyes, and the mouth-parts. The antennas are short, 

and usually consist each of seven segments. The eyes are usually 

represented by a group of ocelli on each side of the 

head; but the ocelli vary greatly in ntimber, and are '^ 

sometimes absent. The mouth-parts consist of an P 

upper lip or labrum; a pair of mandibles; and a pair 

of jaws, which are united at the base, forming a large 

plate, which is known as the gnaihochilarium. In 

the genus Polyxenus there is a pair of lobes between s 

the mandibles and the gnathochilarium, which have 

been named the maxillulcB. (paragnatha?). 

The labrum is merely the anterior part of the ^j^- '^9-— A mandi- 

11 r .1 1 -1 1 • • • Die of Julus; c, 

upper wall of the head and, as m insects, is not an cardo; d,d,teeth; 

appendage. The mandibles, in the forms in which ^' muscle; ma, 

they are best developed, are fitted for biting, and nate ' plate; s, 

consist of several parts (Fig. 19) ; but in some forms ? ^f^i^ ^ (After 

they are vestigial. The gnathochilarium (Fig. 20) is 

complicated in structure, the details of which vary greatly in different 

genera. 






Pig. 20. — The gnathochilarium or second jaws of three diplopods; A, Spirostrtp- 
tus; B, Julus; C, Glomeris: c, cardo; h, liypostoma; Ig, linguce; m, ment'om. 
pm, promentum; st, stipes (After Silvestri). 



CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 17 




In one subdivision of the class Diplopoda, which is represented 
by the genus Polyxenus and a few others, the mandibles are one- 
jointed; and be- 
mxt tween the mandi- 

»'^-l'> ' bles and the 

gnathochilarium 
there is a pair of 
one-jointed lobes, 
which have not 
been found in 
other diplopods; 
these are the "max- 
illulas" (Fig. 21). 
The correspondence 
of the parts of the 
gnathochilarium of 
Polyxenus and its 
allies with the parts 
of the gnathocil- 
larium of other di- 
plopods has not 
been satisfactorily 
determined. 
Most of our more common millipedes possess stink-glands, which 
open by pores on a greater or less nimiber of the body segments. 
These glands are the only means of defence possessed by millipedes, 
except the hard cuticula protecting the body. 

The millipedes as a rule are harmless, living in damp places and 
feeding on decaying vegetable matter; but there are a few species 
that occasionally feed upon growing plants. 

For a more detailed account of the Diplopoda see Pocock ('11). 



Fig. 21. — The second pair of jaws, maxillulae, and the 
third pair of jaws, maxillas or gnathochilarium, of 
Polyxenus; the parts of the maxillae or gnathochila- 
rium are stippled and some are omitted on the right 
side of the figure: mh, basal membrane of the labium ; 
la, "labium" of Carpenter, perhaps the mentum and 
promentum of the gnathochilarium; mx, basal seg- 
ment of the maxilla, perhaps the stipes of the 
gnathochilarium; w:x;. /o, lobe of the maxilla; mx.p, 
maxillary palpus; A, tongue or hypopharynx; mxl, 
maxillula; fl. flagellate process (After Carpenter). 



18 



AN INTRODUCTION TO ENTOMOLOGY 



Class PAUROPODA 

The Pauropods 

The members of this class are small arthropods in which the head is 
distinct, and the segments of the body form a single continuous region. 
Most of the body-segments bear each a single pair of legs. Although 
most of the terga of the body-segments are usually fused in couples, the 
legs are not grouped in double pairs as in the Diplopoda. The antennce 
are branched. The reproductive organs open in the third segment back 
of the head. 

The Pauropoda or pauropods are minute creatures, the described 
species measuring only about one twenty-fifth inch in length, more 
or less. They resemble centipedes in the elongated form of the body 
and in the fact that the legs are not grouped in double pairs as in the 
Diplopoda, although the terga of the body-region are usually fused in 
couples. These characteris- 
tics are well-shown by the 
dorsal and ventral views of 
Pauropus (Fig. 22 and 23). 
Although the pauropods 
resemble the chilopods in 
the distribution of their legs, 
they differ widely in the 
position of the openings of 
the reproductive organs. 
These open in the third seg- 
ment back of the head ; that 
of the female is single, those 
of the male are double. 

The head is distinct from 
the body-region. It bears 
one pair of antennae and two 
pairs of jaws; the eyes are 
absent but there is an eye- 
like spot on each side of the 
head (Fig. 24). The first 
pair of jaws are large, one- 
jointed mandibles; the 
second pair are short pear-shaped organs. Between these two pairs 





Fig. 22. — A pauropod, 
Pauropus huxleyi, dor- 
sal aspect (After Ken- 
yon). 



Fig. 23. — Pauropus 
huxleyi, ventral 
aspect (After 
Lubbock). 



CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 19 




Fig. 24 — Eurypauropus spina- 
sus; face showing the base of 
the antennas, the mandibles, 
and the eye-lilce spots (After 
Kenyon) . 



of jaws, there is a horny framework forming a kind of lower Hp to the 
mouth (Fig. 25). The homologies of the mouth-parts with those of 
the allied classes of arthropods have not 
been determined. 

The body-region consists of twelve 
segments. This is most clearly seen by 
an examination of the ventral aspect of 
the body. When the body is viewed from 
above the mmiber of segments appears to 
be less, owing to the fact that the terga of 
the first ten segments are fused in 
couples. Nine of the body-segments bear 
well-developed legs. The appendages of 
the first segment are vestigial, and the 
last two segments bear no appendages. 
The most distinctive feature of mem- 
bers of this class is the form of the 
antennae, which differ from those of all 
other arthropods in structure. Each 
antenna (Fig. 26) consists of four short 
basal segments and a pair of one-jointed 
branches borne by the fourth segment. 
One of these branches bears a long, many- 
ringed filament with a rounded apical 
knob; and the other branch bears two 
such filaments with a globular or pear- 
shaped body between them. This is prob- 
ably an organ of special sense. 

The pauropods live under leaves and 

stones and in other damp situations. 

Representatives of two quite distinct families are found in this 

country and in various other parts of the world. In addition to these 

a third family, the 

BrachypauropodidcB, 

is foimd in Europe. 

In this family the 

pairs of terga consist 

each of two distinct 

plates. Our two 

„. ^ A .. r 17 . . .■ families are the fol- 

rig. 26. — Antenna 01 hurypauropus spmosus 

(After Kenyon) . lowmg : 




Fig. 25. — Mouth-parts of Eury- 
pauropus ornatus; md, man- 
dible; mx, second iaws; /, 
lower lip (After Latzel). 




20 AN INTROD UCTION TO ENTOMOLOG Y 

Family Pauropodidce. — In members of this family the head is 
not covered by the first tergal plate and the anal segment is not 
covered by the sixth tergal plate. 

The best known representatives of this 
family belong to the genus Pauropus (Fig. 
22). This genus is widely distributed, represen- 
tatives having been found in Europe and in both 
North and South America. They are active, 
measure about one twenty-fifth inch in length, 
"s^^^ and are white. 




Family EiirypauropidcB. — The members of 

this family are characterized by the wide form 

of the body, which bears some resemblance to 

that of a sow-bug. The head is concealed by the 

first tergum of the body-region; and the anal 

segment, by the penultimate tergum. Our most 

familiar representative is Eiirypanropus spinosus 

^'l-^7.—Euryparcro- (pig_ ) ^^is, unlike Pauropus, is slow in its 
pus spinosus (After ^ »^ ' ^ -r > 

Kenyon). movements. 

Class CHILOPODA 
The Centipedes or Chilopods 

The members of this class are air-breathing arthropods in which the 
head is distinct, and the remaining segments of the body form a continuous 
region. The numerous pairs of legs are not grouped in double pairs, as 
in the Diplopcda. The antennae are long and many-jointed. The 
appendages of the first body-segment are jaw-like and function as organs 
of offense, the poison-jaws. The opening of the reproductive organs is 
in the next to the last segment of the body. 

The animals constituting the class Chilopoda or chilopods are 
commonly known as centipedes. They vary to a considerable degree 
in the form of the body, but in all except perhaps the sub-class 
Notostigma the body-segments are distinct, not grouped in couples 
as in the diplopods (Fig. 28). They are sharply distinguished from 
the three preceding classes in the possession of poison-jaws and in 
having the opening of the reproductive organs at the caudal end of 
the body. 

The antennae are large, flexible, and consist of fourteen or more 
segments. There are four pairs of jaws including the jaw-like 



CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 21 




appendages of the first body-segment. These are the mandibles 
(Fig. 29, A), which are stout and consist each of two segments; the 
maxillcs (Fig. 29, B, a), which are foHaceous, 
and usually regarded as biramous; the second 
maxill(B or palpognaihs, which are leg-like in 
form, consisting of five or six segments, and 
usually have the coxae united on the middle 
line of the body (Fig. 29, B, 6), and the poison- 
claws or toxicognaths, which are the appendages 
of the first body-segment (Fig. 29, C). 

The poison-claws consist each of six seg- 
ments, of which the basal one, or coxa is usually 
fused with its fellow, the two forming a large 
coxal plate, and the distal one is a strong pierc- 
ing fang in which there is the opening of the 
duct leading from a poison gland, which is in 
the appendage. 

The legs consist typically of six segments, 

of which the last, the tarsus, is armed with a 

-A centipede single terminal claw. The last pair of legs are 

directed backwards, and are often greatly 

modified in form. 

The class Chilopoda includes two quite distinct groups of animals 

which are regarded by Pocock ('11) as sub-classes, the Pleuro- 

stigma and theNoto- 

stigma. The names I^J^. J^%.^\ C 

of the sub-classes 
refer to the position ^ a 
of the spiracles. 

Sub-Class 
PLEUROSTIGMA 

The typical Centipedes 

In the typical cen- 
tipedes, the sub-class 
Pleurostigma, the 
spiracles are paired 
and are situated in the sides of the segments that bear them. Each 
leg-bearing segment contains a distinct tergiim and sternum, the 
number of sterna never exceeding that of the terga. The eyes 



Buthropolys multi- 
dentatus. 




Fig. 29. — Mouth-parts of a centipede, Geophilus flavi' 
dus. A, right mandible, greatly enlarged. B, the 
two pairs of maxillae, less enlarged; a, the united 
00X33 of the maxillse; b, the united coxae of the 
second maxillae or palpognaths. C, the poison claws 
or toxicognaths (After Latzel) 



22 



AN INTRODUCTION TO ENTOMOLOGY 



when present are simple ocelli; but there may be a group of ocelli 
on each side of the head. Figure 28 represents a typical centipede. 




Sub-Class NOTOSTIGMA 

Scutigera and its Allies 

In the genus Scuttgera and its allies, 
which constitute the sub-class Notostigma, 
there is a very distinctive type of respiratory- 
organs. There is a single spiracle in each 
of the spiracle-bearing segments, which are 
seven in number. These spiracles open in 
the middle line of the back, each in the hind 
margin of one of the seven prominent terga 
cf the body-region. Each spiracle leads into 
a short sac from which the tracheal tubes 
extend into the pericardial blood-sinus. 

There are fifteen leg-bearing segments in 
the body region; but the terga of these 
segments are reduced to seven by fusion and 
suppression. 

The eyes differ from those of afl other 
members of the old group Myriapoda in 
being compoimd, the ommatidia resembling 
in structure the ommatidia of the compound 
eyes of insects. 

The following species is the most familiar 
representative of the Notostigma. 

The house centipede, Scutigera forceps. — 
This centipede attracts attention on account 
of the great length of its appendages 
(Fig. 30), and the fact that it is often seen, 
in the regions where it is common, running on the walls of rooms in 
dwelling houses, where it himts for flies and other insects. It prefers 
damp situations; in houses it is most frequently foimd in cellars, 
bathrooms, and closets. Sometimes it becomes very abundant in 
conservatories, living among the stored pots and about the heating 
pipes. It is much more common in the South than in the North. 



Fig. 30. — Scutigera forceps. 



CHARA CTERISTICS OF INSECTS A ND THEIR RELA TI VES 23 



The body of the adult measures an inch or a little more in 
length. It is difficult to obtain perfect specimens, as they shed 
their legs when seized. 

Class SYMPHYLA 

The Symphylids 

The members of this class are small 
arthropods in which the head is distinct, and 
the segments of the body form a single con- 
tinuous region. Most of the body-segments 
bear a single pair of legs. The antenncB are 
very long and many-jointed. The head bears 
a Y-shaped epicranial suture, as in insects. 
The opening of the reproductive organs is in 
the third segment behind the head. 

The class Symphyla includes a small 
number of many-legged arthropods which 
exhibit striking affinities with insects, and 
especially with the Thysanura. The body 
is centipede-Hke in form (Fig. 31). The 
head is distinct, and is not bent down 




Fig . 31. — Scolopendrella 
(After Latzel). 



as it is in the diplopods and pauro- 
pods; it is shaped as in Thysanura and 
bears a Y-shaped epicranial suture. The 
body-region bears fifteen terga, which are 
distinct, not grouped in couples as in the 
two preceding classes; and there are 
eleven or twelve pairs of legs. 

The antennae are long and vary greatly 
in the number of the segments. There are 
no eyes. The mandibles, the "maxillulae" 
(paragnatha) , the maxillae, and the sec- 
ond maxillae or labium are present. 




Fig. 32. — Mouth-parts of 
Scolopendrella seen from 
below; md, mandible; mx, 
maxillae; s, stipes; p, pal- 
pus; /, second maxillee or 
labium. The mandible on 
the right side of the figure 
is omitted (After Hansen). 



The mandibles (Fig. 32, md) are two- 
jointed; the maxillulcB (Fig. 33, m) are 

small, not segmented, and are attached to a median lobe or 
hypopharynx (Fig. 33, h); they are hidden when the mouth-parts 
are viewed from below as represented in Figure 3 2 ; the maxillce (Fig. 





24 AN INTRODUCTION TO ENTOMOLOGY 

2,2, mx) resemble in a striking degree the maxillae of insects, consisting 
of a long stipes, (5), which bears a minute palpus, {p), and an outer 
and inner lobe ; the second maxillce or labium (Fig. 
32,/) also resembles the corresponding part of the 
more generalized insects, being composed of a pair 
of united gnathites. 

The legs of the first pair are reduced in size and 
in the number of their segments. The other legs ^^pophl'i^i^^^ ^h) 
consist each of five segments; the last segment andmaxillulaeCm) 
bears a pair of claws. Excepting the first two (Iftt/'filntent 
pairs of legs, each leg bears on its proximal seg- 
ment a slender cylindrical process, the parapodium (Fig. 34, p). 
These parapodia appear to correspond with the styli of the 
Thysanura. 

At the caudal end of the body there is a pair of 
appendages, which are believed to be homologous 
/ '■"^^^^rfH^ with the cerci of insects (Fig. 35, c). 

A striking peculiarity of the symphylids is that 

Fig- 34-— A ieg of ^-j^gy possess only a single pair of tracheal tubes, 
Scolopendrella; ,., , . ff, . ^ . 

/>, parapodium. which Open by a pair of spiracles, situated in the 

head beneath the insertion of the antennae. 

The members of this class are of small size, the 
larger ones measiuing about one-fourth inch in 
length. They live in earth under stones and decay- 
ing wood, and in other damp situations. Imma- 
ture individuals possess fewer body-segments 
and legs than do adults. 

Less than thirty species have been described; 
but doubtless many more remain to be discovered. 

The known species are classed in two genera : pig. j^.—The caudal 
Scolopendrella and Scutigerella. In the former the ^nd of the body of 

, . ^ r j_, j_ 1 -1 •, Scolopendrella; I, 

posterior angles of the terga are produced and leg; c, cercus (After 
angular; while in the latter they are rounded. Latzel). 

A monograph of the Symphyla has been published by Hansen ('03). 



Class MYRIENTOMATA 

Professor Comstock, in the former editions of this book, gave this 
group of arthropods the rank of a class, coordinate with the other 
classes of the Arthropoda. 

The position and rank of these animals were uncertain at the 
time the Introduction was written. Indeed, the affinities of the 




CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 25 



Protura are not yet clearly understood, but the general opinion 
among morphologists and sys- 
tematists is tending more and 
more to place these tiny crea- 
tures in an ordinal group, the 
Protura, among the insects in the 
class Hexapoda. It has seemed 
best to follow this general trend 
and we have, therefore, trans- 
ferred this group to the class 
Hexapoda, order Protura, on p. 
220. 

In commenting on the posi- 
tion of the group in the original 
edition of the Introduction, Pro- 
fessor Comstock gave the follow- 
ing discussion and explanation of 
his conclusions at that time : 

"The first discovered species 
was described in 1907 by Profes- 
sor F. Silvestri of Portici, who 
regarded it as the type of a dis- 
tinct order of insects, for which 
he proposed the name Protura. 
Later Professor Antonio Berlese 
of Florence described several 
additional species, and pubHshed pjg_ ^e.—Acerentomon doderoi: A, dor- 
an extended monograph of the sal aspect; B, ventral aspect; 1, 1, 1, 

A /-D ^ > z,\ vestigial abdominal legs (After 

order (Berlese 09 h). Berime). 

"Professor Berlese concluded 
that these arthopods are more closely allied to the Myriapoda and 
especially to the Pauropoda than they are to the insects, and changed 
the name of the order, in an arbitrary manner, to Myrientomata. 

"It seems clear to me that in either case whether the order is classed 
among the insects or assigned to some other position it should be 
known by the name first given to it, that is, the Protura. 

"In the present state of our knowledge of the affinities of the classes 
of arthropods, it seems best to regard the Protura as representing a 
separate class, of rank equal to that of the Pauropoda, Symphyla, 
etc.; and for this class I have adopted the name proposed for the 
group by Berlese, that is the Myrientomata." 




26 AN INTRODUCTION TO ENTOMOLOGY 

Class HEXAPODA 
The Insects 

The members of this class are air-breathing arthropods, with distinct 
head, thorax, and abdomen. They have one pair of antennae, three pairs 
of legs, and usually one or two pairs of wings in the adult state. The 
opening of the reproductive organs is near the caudal end of the body. 

We have now reached in our hasty review of the classes of arthro- 
pods the class of animals to which this book is chiefly devoted, the 
Hexapoda,* or Insects, the study of which is termed entomology. 

The number of species of insects now known is around 600,000, 
perhaps more rather than less. The number of species yet undescribed 
is purely problematical. Probably there are hundreds of thousands 
of unknown forms distributed over the tropical portions of the earth. 

Insects vary greatly in size. Folsom says that some insects 
are smaller than the largest protozoans, while some are larger than 
the smallest vertebrates. A beetle, Dynastes hercules from Vene- 
zuela, which may be 155mm. long, and a Venezuelan grasshopper, 
Tropidacris latreillei, which may attain a length of i66mm., are 
among the largest insects. Some moths of the genus Attacus may 
have a wing expanse of from 240 to 2 5 5mm. while a BraziHan noctuid, 
Erebus agrippina, is said to have a wing expanse of 280mm. On the 
other hand, certain beetles of the family Trichopterygidae may be 
but .25mm. in length, and some hymenopterous egg parasites are 
even smaller. 

Insects are essentially terrestrial ; and in the struggle for existence 
they are the most successful of all terrestrial animals, outnumbering 
both in species and individuals all others together. On the land they 
abound under the greatest variety of conditions, special forms having 
been evolved fitted to live in each of the various situations where 
other animals and plants can live; but insects are not restricted to 
dry land, for many aquatic forms have been developed. 

The aquatic insects are almost entirely restricted to small bodies 
of fresh water, as streams and ponds, where they exist in great num- 
bers. Larger bodies of fresh water and the seas are nearly destitute 
of them except at the shores. 

*Hexapoda: hex (?|), six', pons (ttoi/s), a foot. 



CHARACTERISTICS OF INSECTS AND THEIR RELA TIVES 27 



As might be inferred from a consideration of the immense number 
of insects, the part they play in the economy of nature is an exceed- 
ingly important one. Whether this part is to be considered a bene- 
ficial or an injurious one when judged from the human standpoint 
would be an exceedingly difificult question to determine. For if 
insects were to be removed from the earth the whole face of nature 
would be changed. 

While the removal of insects from the earth would eliminate many 
pests that prey on vegetation, would relieve many animals of annoying 
parasites, and would remove some of the most terrible diseases to 
which oiu- race is subject, it would result in the destruction of many 
groups of animals that depend, either 
directly or indirectly, upon insects for food, 
and the destruction of many flowering 
plants that depend upon insects for the 
fertilization of their blossoms. Truly this 
world would speedily become a very differ- 
ent one if insects were exterminated. 

It may seem idle to consider what 
would be the result of the total destruction 
of insects; but it is not wholly so. A care- 
ful study of this question will do much 
to open our eyes to an appreciation of the 
wonderful "web of life" of which we are a 
part. 

Most adult insects can be readily dis- 
tinguished from other arthropods by the 
form of the body, the segments being grouped into three distinct 
regions, head, thorax, and abdomen (Fig. 37), by the possession of 
only three pairs of legs, and in most cases by the presence of wings. 

The head bears a single pair of 
antennas, the organs of sight, and the 
mouth-parts. To the thorax, are 
articulated the organs of locomotion, 
the legs and the wings when they are 
present. The abdomen is usually 
without organs of locomotion but 
frequently bears other appendages at 
the caudal end. 

These characteristics are also possessed by the immature forms 
of several of the orders of insects ; although with these the wings are 




Fig. 37. — Wasp with head, 
thorax, and abdomen 
separated. 




Fig. 38. — Nymph of the red- 
legged locust. 



28 



AN INTRODUCTION TO ENTOMOLOGY 



rudimentary (Fig. 38). But in other orders of insects the immature 
forms have been greatly modified to adapt them to special modes of 
life, with the result that they depart widely from the insect type. For 
example, the larvae of bees, wasps, flies, and many beetles are legless 
and more or less worm-like in form (Fig. 4) ; while the larvae of butter- 
flies and moths possess abdominal as well as thoracic legs (Fig. 39). 




Fig- 39-~~A. larva of a handmaid moth, Datana. 



Although the presence of wings in the adult state is characteristic 
of most insects, there are two orders of insects, the Thysanura and 
the CoUembola, in which wings are absent. These orders represent 
a branch of the insect series that separated from the main stem before 
the evolution of wings took place; their wing- 
less condition is, therefore, a primitive one. 
There are also certain other insects, as the lice 
and bird-lice, that are wingless. But it is 
believed that these have descended from 
winged insects, and have been degraded by 
their parasitic life; in these cases the wingless 
condition is an acquired one. Beside these 
there are many species belonging to orders in 
which most of the species are winged that 
have acquired a wingless condition in one or 
both sexes. Familiar examples of these are the 
females of the Coccidas (Fig. 40), and the 
females of the canker-worm moths. In fact, 
wingless forms occur in most of the orders of 
winged insects. 

As the structure and transformations of insects are described in 
detail in the following chapters, it is unnecessary to dwell farther on 
the characteristics of the Hexapoda in this place. 




Fig. 40. — A mealy-bug, 
Dactylopius. 



CHAPTER II. 
THE EXTERNAL ANATOMY OF INSECTS 

I. THE STRUCTURE OF THE BODY-WALL 




a. THE THREE LAYERS OF THE BODY-WALL 

Three, more or less distinct, layers can be recognized in the body- 
wall of an insect: first, the outer, protecting layer, the cuticula; 
second, an intermediate, cellular layer, the hypodermis; and third, an 
inner, delicate, membranous layer, the basement membrane. These 

layers can be distinguished 
only by a study of carefully 
prepared, microscopic sec- 
tions of the body- wall. 
Figure 41 represents the ap- 
pearance of such a section. 
As the outer and inner layers 
are derived from the hypo- 
dermis, this layer will be 
described first. 

The hypodermis. — The ac- 
tive living part of the body- 
wall consists of a layer of cells, 
which is termed the hypo- 
dermis (Fig. 41, /^). 

The hypodermis is a portion of one of the germ-layers, the ectoderm. In 
other words, that portion of the ectoderm which in the course of the development 
of the insect comes to form a part of the body- wall is termed the hypodermis; 
while to invaginated portions of the ectoderm other terms are appHed, as the 
epithehal layer of the trachea?, the epithelial layer of the fore-intestine, and the 
epithelial layer 01 the hind-intestine. 

The cells of which the hypodermis is composed vary in shape ; but 
they are usually columnar in form, constituting what is known to 
histologists as a columnar epithelium. Sometimes the cells are so 
flattened that they form a simple pavement epithelium. I know of 
no case in which the hypodermis consists of more than a single layer 
of cells; although in wing-buds and buds of other appendages, where 
the cells are fusiform, and are much crowded, it appears to be irregu- 

(29) 



Fig. 41. — A section of the body- wall of 
an insect: c, cuticula; h, hypodermis; 
hm, basement membrane; e, epidermis, 
d, dermis; tr, trichogen; s, seta. 



30 AN INTROD UCTION TO ENTOMOLOG V 

larly stratified. This is due to the fact that the nuclei of the different 
cells are at different levels. 

The Trichogens. — Certain of the hypodermal cells become highly- 
specialized and produce hollow, hair-like organs, the setae, with 
which they remain connected through pores in the cuticula. Such a 
hair-forming cell is termed a trtchogen (Fig. 41, tr)\ and the pore in 
the cuticula is termed a Mchopore. 

The cuticula. — Outside of the hypodermis there is a firm layer 
which protects the body and serves as a support for the internal 
organs; this is the cuticula (Fig. 41, c). The cuticula is produced by 
the hypodermis; the method of its production is discussed on p. 171, 
where the molting of insects is treated. The cuticula is not destroyed 
by caustic potash; it is easy, therefore, to separate it from the tissues 
of the body by boiling or soaking it in an aqueous solution of this 
substance. 

Chitin. — This word was introduced into entomology by Odier in 
1823 for the colorless, flexible covering of the arthropods after the 
integument had been boiled in caustic potash and the albuminous, 
oily, coloring and mineral substances had been removed thereby. 
By a not unusual turn in the use of words, chitin has come to mean, 
as stated by Newport (1836-1839): "The peculiar substance that 
constitutes the hard portion of the dermo-skeleton [in insects]." 
From 1870 and onward the words chitinize and chitinization have 
come to mean the hardening of the cuticula by the incorporation of 
chitin; and they are used with that meaning throughout this work. 
(For references to chitin, see p. 10 10). 

Rigid and flexible cuticula. — When freshly formed by the hypo- 
dermis, the cuticula is flexible and elastic, and certain portions of it, 
as at the nodes of the body and of the appendages, remain so. But 
the greater part of the cuticula, especially in adult insects, usually 
becomes firm and inelastic; this is due to a change in which the 
hardening substance is developed within or upon the original soft 
cuticula. What the exact nature of this change is or how it is pro- 
duced is not known. This change is usually spoken of as chitinization ; 
and the hard parts of the cuticula are then said to be chitinized, and 
the soft parts, as at the nodes, non-chitinized. The hardened or 
chitinized cuticula is rigid and inelastic while the soft or non-chitinized 
cuticula is flexible and elastic. The elasticity of the soft cuticula is 
well shown by the stretching of the body wall after a molt. It is 
also strikingly shown by the expansion of the soft, intersegmental 
cuticula to accommodate the growing eggs, as in the queens of 
Termites. 



THE EX TERN A L ANATOMY OF INSE CTS 3 1 

The formation of chitin is not restricted to the hypodermis, but is 
a property of the invaginated portions of the ectoderm; the fore- 
intestine, the hind-intestine, and the tracheee are all lined with a 
cuticular layer, which is continuous with the cuticula of the body-wall 
and is chitinized. The most marked case of internal formation of 
chitin is the development of large and powerful teeth in the proven- 
triculus of many insects. 

The epidermis and the dermis. — Two quite distinct parts of the 
cuticula are recognized by recent writers ; these are distinguished as 
the epidermis and the dermis respectively. 

The epidermis is the external portion ; in it are located all of the 
cuticular pigments; and from it are formed all scales, hairs, and other 
surface structures. It is designated by some writers as the primary 
cuticula (Fig. 41, e). 

The dermis is situated beneath the epidermis. It is formed in 
layers, which give sections of the cuticula the well-known laminate 
appearance. It is sometimes termed the secondary cuticula (Fig. 41, <^)- 

The basement membrane. — The inner ends of the hypodermal cells 
are bounded by a more or less distinct membrane ; this is termed the 
basement membrane (Fig. 4 1 , bm) . The basement membrane is most 
easily seen in those places where the inner ends of the hypodermal cells 
are much smaller than the outer ends ; here it is a continuous sheet 
connecting the tips of the hypodermal cells. 

b. THE EXTERNAL APOPHYSES OF THE CUTICULA 

The outer surface of the cuticula bears a wonderful variety of pro- 
jections. These, however, can be grouped under two heads: first, 
those that form an integral part of the cuticula; and second, those 
that are connected with the cuticula by a joint. Those that form an 
integral part of the cuticula are termed apophyses; those that are con- 
nected by a joint are termed appendages of the cuticula. 

The cuticular nodules. — The most frequently occurring out- 
growths of the cuticula are small, more or less conical nodules. 
These vary greatly in size, form, and distribution over the surface of 
the body in different species of insects, and are frequently of 
taxonomic value. 

The fixed hairs. — On the wings of some insects, as the Trichoptera 
and certain of the Lepidoptera, there are in addition to the more 
obvious setse and scales many very small, hair-like structures, which 



32 



AN INTRODUCTION TO ENTOMOLOGY 



differ from setae in being directly continuous with the cuticula, and 
not connected with it by a joint; these are termed the fixed hairs, or 
aculese. The mode of origin and development of the fixed hairs has not 
been studied. 

The spines. — The term spine has been used loosely by writers on 
entomology. Frequently large setae are termed spines. In this work 
such setae are called spine-like setse; and the term spine is applied 
only to outgrowths of the cuticula that are not separated from it by a 
joint. Spines differ also from spine-like setae in being produced by 
undifferentiated hypodermal cells and are usually if not always of 
multicellular origin, while each seta is produced by a single trichogen 
cell. The accompanying diagram (Fig. 42) illustrates this difference. 



C. THE APPENDAGES OF THE CUTICULA 

Under this head are included those outgrowths of the cuticula that 
are connected with it by a joint. Of these there are two quite dis- 
tinct types represented by the spurs and the setas respectively. 

The spurs. — There exist upon the legs of many insects appendages 
which on account of their form and position have been termed spurs. 
Spurs resemble the true spines described above and differ from setas 
in being of multicellular origin; they differ from spines in being 

appendages, that is, in 
being connected with the 
body-wall by a joint. 

The setae. — The setae 
are what are commonly 
called the hairs of in- 
sects. Each seta (Fig. 
42, s) is an appendage of 
the body- wall, which 
arises from a cup-like 
cavity in the cuticula, 
the alveolus, situated at 
the outer end of a per- 
foration of the cuticula, 
the trtchopore; and each 
seta is united at its base with the wall of the trichopore by a ring of 
thin membrane, the articular membrane of the seta. 

The setae are hollow ; each is the product of a single hypodermal 
cell, a trichogen (Fig. 42), and is an extension of the epidermal 
layer of the cuticula. 




Fig. 42. — Diagram illustrating the diflference be- 
tween a spine (sp) and a seta (s). 



THE EXTERNAL ANATOMY OF INSECTS 33 

In addition to the trichogen there may be a gland-cell opening into 
the seta, thus forming a glandular hair, or a nerv^e may extend to the 
seta, forming a sense-hair; each of these types is discussed later. 

The most common type of seta is bristle-like in form; familiar 
examples of this type are the hairs of many larvae. But numerous 
modifications of this form exist. Frequently the setae are stout and 
firm, such are the spine-like setcB; others are furnished with lateral 
prolongations, these are the plumose hairs; and still others are flat, 
wide, and comparatively short, examples of this form are the scales 
of the Lepidoptera and of many other insects. 

The taxonomic value of setcB. — In many cases the form of the setae 
and in others their -arrangement on the cuticula afford useful charac- 
teristics for the classification of insects. Thus the scale-like form of 
the setas on the wing-veins of mosquitoes serves to distinguish these 
insects from closely alHed midges; and the clothing of scales is one 
of the most striking of the characteristics of the Lepidoptera. 

The arrangement of the setas upon the cuticula, in some cases at 
least, is a very definite one. Thus Dyar ('94) was able to work out a 
classification of lepidopterous larvai by a study of the setas v\.ith 
which the body is clothed. 

A classifu,ation of setce. — If only their function be considered the 
hairs or setae of insects can be grouped in the three following classes ; 

(i) The clothing hairs. — Under this head are grouped those hairs 
and scales whose primary function appears to be merely the- protection 
of the body or of its appendages. So far as is known, such hairs con- 
tain only a prolongation of the trichogen cell that produced them. It 
should be stated, however, that this group is merely a provisional one; 
for as yet comparatively little is known regarding the relation of these 
hairs to the activities of the insects possessing them. 

In some cases the clothing hairs have a secondary fimction. Thus 
the highly specialized overlapping scales of the wings of Lepidoptera. 
which are modified setae, may serv^e to strengthen the wings; and the 
markings of insects are due almost entirely to hairs and scales. The 
fringes on the wmgs of many insects doubtless aid in flight, and the 
fringes on the legs of certain aquatic insects also aid in locomotion. 

(2) The glandular hairs. — Under this head are grouped those hairs 
that serve as the outlets of gland cells. They are discussed in the next 
chapter, imder the head of hypodermal glands. 

(3) The sense-hairs — In many case a seta, more or less modified 
in form, constitutes a part of a sense-organ, either of touch, taste, or 
smell : examples of these are discussed in the next chapter. 



34 AN INTRODUCTION TO ENTOMOLOGY 

d. THE SEGMENTATION OF THE BODY 

The cuticular layer of the body-wall, being more or less rigid, 
forms an external skeleton; but this skeleton is flexible along certain 
transverse lines, thus admitting of the movements of the body, and 
producing the jointed appearance characteristic of insects and of 
other arthropods. 

An examination of a longitudinal section of the body-wall shows 
that it is a continuous layer and that the apparent segmentation is due 
to infoldings of it (Fig. 43), 

The body-seg- 
ments, somites, or 
metameres . — Each 

section of the body „. ^. , , . ,. . ^. , ^, 

r 1 Fi?- 43- — Diagram of a longitudinal section of the 

between two of the body-wall of an insect. 

infoldings described 

above is termed a body-segment, or somite, or metamere. 

The transverse conjunctivae. — The infolded portion of the body- 
wall connecting two segments is termed a conjunctiva. These con- 
junctivae may be distinguished from others described later as the 
transverse conjunctivce. 

The conjunctivae are less densely chitinized than the other portions 
of the cuticula; their flexibility is due to this fact, rather than to a 
comparative thinness as has been commonly described. 

e. THE SEGMENTATION OF THE APPENDAGES 

The segmentation of the legs and of certain other appendages is 
produced in the same way as that of the body. At each node of an 
appendage there is an infolded, flexible portion of the wall of the 
appendage, a conjunctiva, which renders possible the movements of 
the appendage. 

/. THE DIVISIONS OF A BODY-SEGMENT 

In many larvae, the cuticula of a large part of the body-wall is of 
the non-chitinized type ; in this case the wall of a segment may form 
a ring which is not divided into parts. But in most nymphs, naiads, 
and adult insects, there are several densely chitinized parts in the wall 
of each segment; this enables us to separate it into well-defined 
portions. 

The tergum, the pleura, and the sternum. — The larger divisions of 
a segment that are commonly recognized are a dorsal division, the 



THE EXTERNAL ANATOMY OF INSECTS 35 

tergum; two lateral divisions, one on each side of the body, the pleura; 
and a ventral division, the sternum. 

Each of these divisions may include several definite areas of 
chitinization. In this case the sclerites of the tergum are referred to 
collectively as the tergites, those of each pleurum, as the pleurites, and 
those constituting the sternum, as the sternites. 

The division of a segment into a tergum, two pleura, and a sternum 
are most easily seen in the wing-bearing segments, but it can be 
recognized also in the prothorax of certain generalized insects. This 
is especially the case in many Orthoptera, as cockroaches and walking- 
sticks, where the pleura of the prothorax are distinct from the tergum 
and the sternum. In the abdomen it is evident that correlated with 
the loss of the abdominal appendages a reduction of the pleura has 
taken place. 

The lateral conjunctivae. — On each side of each abdominal segment 
of adults the tergum and the sternum are united by a strip of non- 
chitinized cuticula; these are the lateral conjtmctivae. Like the 
transverse conjunctivee, the lateral ones are more or less infolded. 

The sclerites. — Each definite area of chitinization of the cuticula 
is termed a sclerite. 

The sutures. — The lines of separation between the sclerites are 
termed sutures. Sutures vary greatly in form ; they may be infolded 
conjunctiva; or they may be mere lines indicating the place of union 
between two sclerites. Frequently adjacent sclerites grow together 
so completely that there is no indication of the suture ; in such cases 
the suture is said to be obsolete. 

The median sutures. — On the middle line of the tergites and also of 
the sternites there frequently exist longitudinal sutures. These are 
termed the median sutures. They represent the lines of the closure 
of the embryo, and are not taken into account in determining the 
number of the sclerites. 

The dorsal median suture has been well-preserved in the head and 
thorax, as it is the chief line of rupture of the cuticula at the time of 
molting. 

The piUf erous tubercles of larvae. — The setae of larvae are usually 
borne en slightly elevated annular sclerites; these are termed pilif- 
erous tubercles. 

The homologizing of the sclerites. — While it is probable that the 
more important sclerites of the body in winged insects have been 
derived from a common winged ancestor and, therefore, can be 
homologized, miany secondary sclerites occur which can not be thus 
homoiogized. 



36 AN INTRODUCTION TO ENTOMOLOGY 

g. THE REGIONS OF THE BODY 

The segments of the body in an adult insect are grouped into three, 
more or less well-marked regions: the head, the thorax, and the 
abdomen. Each of these regions consists of several segments more or 
less closely united. 

The head is the first of these regions; it bears the mouth-parts, 
the eyes, and the antennas. The thorax is the second region ; it bears 
the legs and the wings if they are present. The abdomen is the third 
region; it may bear appendages connected with the organs of repro- 
duction. 

II. THE HEAD 

The external skeleton of the head of an insect is composed of 
several sclerites more or less closely united, forming a capsule, which 
includes a portion of the viscera, and to which are art'culated certain 
appendages. 

a. THE CORNEAS OF THE EYES 

The external layer of the organs of vision, the corneas of the eyes, 
is, in each case, a translucent portion of the cuticula. It is a portion 
of the skeleton of the head, which serves not merely for the admission 
of light but also to support the more delicate parts of the visual 
apparatus. 

The corneas of the compound eyes. — The compound eyes are the 
more commonly observed eyes of insects. They are situated one on 
each side of the head, and are usually conspicuous. Sometimes, as in 
dragon-flies, they occupy the larger part of the surface of the head. 
The compound eyes are easily recognized as eyes; but when one 
of them is examined with a microscope it is found to present an 
appearance very different from that of the eyes of higher animals, its 
surface being divided into a large number of six-sided divisions (Fig. 
44) ; hence the term ccmpound eyes applied to them. 

A study of the internal structure of this organ 
has shown that each of these hexagonal divisions 
is the outer end of a distinct element of the eye. 
Each of these elements is termed an ommattdium. 
The number of ommatidia of which a compound 
p. '^^ ^^ ^^r eye is composed varies greatly; there may be not 
cornea of a com- more than fifty, as in certain ants, or there may 
pound eye. |-,g j^^ny thousand, as in a butterfly or a dragon-fly. 

As a rule, the immature stages of insects with a gradual metamor- 
phosis end also those of insects with an incomplete metamorphosis, 







THE EXTERNAL A NA TOM Y OF INSECTS 37 

that is to say nymphs and naiads possess compound eyes. But the 
larvee of insects with a complete metamorphosis, do not possess well- 
developed compound eyes; although there are frequently a few sep- 
arate ommatidia on each side of the head. These are usually termed 
ocelli ; but the ocelli of larvae should not be confused with the ocelli 
of nymphs, naiads, and adults. 

The corneas of the ocelli. — In addition to the compound eyes most 
nymphs, naiads, and adult insects possess other eyes, which are 
termed ocelli. The cornea of each ocellus is usually a more or less 
nearly circular, convex area, which is not divided into facets. The 
typical number of ocelli is four; but this number is rarely found. 
The usual number is three, a median ocellus, which has been derived 
from a pair of ocelli united, and a distinct pair of ocelli. Frequently 
the median ocellus is lacking, and less frequently, all of the ocelli 
have been lost. The position of the ocelli is discussed later. 

h. THE AREAS OF THE SURFACE OF THE HEAD 

In descriptions of insects it is frequently necessary to refer to the 
different regions of the surface of the head. Most of these regions 
were named by the early insect anatomists; and others have been 
described by more recent writers. 

This terminology is really of comparatively little morphological value; for 
in some cases a named area includes several sclerites, while in others only a portion 
of a sclerite is included. This is due to the fact that but few of the primitive 
sclerites of the head have remained distinct, and some of them greatly over- 
shadow others in their development. The terms used, however, are sufficiently 
accurate to meet the needs of describers of species, and will doubtless continue in 
use. It is necessary, therefore, that students of entomology become familiar 
with them. 

The best landmark from which to start in a study of the areas of 
the surface of the head is the epicranial suture, the inverted Y-shaped 
suture on the dorsal part of the head, in the more generalized insects 
(Fig. 45, e. sit). Behind the arms of this 
suture there is a series of paired sclerites, which 
meet on the dorsal wall of the head, the line of 
union being the stem of the Y, a median suture ; 
and between the arms of the Y and the mouth 
there are typically three single sclerites (Fig. 45, 
F, C, L). It is with these unpaired sclerites 
that we will begin our definitions of the areas 
of the head. ^ Fig. 45.-Head of a 

The front. — The front is the unpaired cricket. 

sclerite between the arms of the epicranial suture (Fig. 45, F). 




38 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. 46.— Head of 
a cockroach; m, 
muscle impres- 
sions. 



In the more generalized insects at least, if not in all, the front 

bears the median ocellus; and in the Plecoptera, the paired ocelli also. 

Frequently the suture between the front and the following sclerite, the 

clypeus, is obsolete ; but as it ends on each side in the invagination 

which forms an anterior arm of the tentorium or 

endo-skeleton (Fig. 46, at), its former position can 

be inferred, at least in the more generalized 

insects, even when no other trace of it remains. 

In Figure 46 this is indicated by a dotted line. 

The clypeus. — The clypeus is the intermediate 
of the three unpaired sclerites between the epi- 
cranial suture and the mouth (fig. 46, c). To this 
part one condyle of the mandible articulates. 

Although the clypeus almost always appears 
to be a single sclerite, except when divided trans- 
versely as indicated below, it really consists of a 
transverse row of three sclerites, one on the median line, and one on 
each side articulating with the mandible. The median sclerite may 
be designated the clypeus proper, and each lateral sclerite, the ante- 
coxal piece of the mandible. Usually there are no indications of the 
sutures separating the clypeus proper from the antecoxal pieces ; but 
in some insects they are distinct. In the larva of Corydalus, the ante- 
coxal pieces are not only distinct but are quite large (Fig. 47, ac, ac). 
In some insects the clypeus is completely or partly divided by a 
transverse suture into two parts (Fig. 45). These may be designated 
as the first clypeus and the second clypeus, respectively; the first 
clypeus being the part next the front (Fig. 
45, Ci) and the second clypeus being that next 
the labrum (Fig. 45, C2). 

The suture between the clypeus and the 
epicranium is termed the clypeal suture. 

The labrum. — The labrum is the movable 
flap which constitutes the upper lip of the 
mouth (Fig. 45, L). The labrum is the last of 
the series of unpaired sclerites between the 
epicranial suture and the mouth. It has the 
appearance of an appendage but is really a 
portion of one of the head segments. 

The epicranium. — Under the term epi- 
cranium are included all of the paired sclerites of the skull, and some- 
times also the front. The paired sclerites constitute the sides of 




Fi^. 47.— Head of a 
larva of Corydalus, 
dorsal aspect. 



THE EXTERNAL ANATOMY OF INSECTS 



39 



the head and that portion of the dorsal surface that is behind the 

arms of the epicranial suture. The sclerites constituting this 

region are so closely united that they were regarded as a single 

piece by Straus-Durckheim (1828), who also included the front in 

this region, the epicranial suture being obsolete in the May beetle, 

which he used as a type. 

The vertex. — The dorsal portion of the epicranium; or, more 

specifically, that portion which is next the front and between the 

compound eyes is known as the vertex (Fig. 45, V, V). In many 

insects the vertex bears the paired ocelli. It is not a definite sclerite; 

but the term vertex is a very useful one and will doubtless be retained. 

The occiput. — ^The hind part of the dorsal surface of the head is the 

occiput. When a distinct sclerite, it is formed 

from the tergal portion of the united postgenae 

described below (Fig. 47, 0, 0). 

The genae. — The gems are the lateral portions 
of the epicranium. Each gena, in the sense in 
which the word was used by the older writers, 
includes a portion of several sclerites. Like 
vertex, however, the term is a useful one. 

The postgenae. — In many insects each gena is 
divided by a well-marked suture. This led the 
writer, in an earher work ('95), to restrict the 
term gena to the part in front of the suture (Fig. 
48, G), and to propose the term postgena for the 
part behind the suture (Fig. 48, Pg). 
The gula. — The gtila is a sclerite forming the ventral wall of the 

hind part of the head in certain orders of insects, 

and bearing the labium or second maxillae (Fig. 

49, Gu). In the more generalized orders, the 

sclerite corresponding to the gula does not form 

a part of the skull. The sutures forming the 

lateral boundaries of the gula are termed the 

gular sutures. 

The ocular sclerites. — In many insects each 

compound eye is situated in the axis of an 

annular sclerite; these sclerites bearing the 

compound eyes are the ocular sclerites (Fig. 50, os). 
The antennal sclerites. — In some insects there 

is at the base of ench antenna an annular sclerite; 

these are the antennal sclerites (Fig. 50, as). The antennal sclerites 

are most distinct in the Plecoptera. 




Fig. 48. — Head and 
neck of a cock- 
roach. 




-Head of 
Coryd'ilus, adult, 
ventral aspect. 




40 AN INTROD UCTION TO ENTOMOLOG Y 

The trochantin of the mandible. — In some insects, as Orthoptera 
there is a distinct sclerite between each mandible and the gena: 
this is the trochantin of the mandible (Fig. 45, tr). 

The maxillary pleurites. — In some of the more generaHzed insects, 
as certain cockroaches and crickets, it can be seen that each maxilla 
is articulated at the ventral end of a pair of sclerites, between which 
is the invagination that forms the posterior arm of the tentorium; 
these are the maxillary pleurites; the pos- 
terior member of this pair of sclerites can 
be seen in the lateral view of the head of a 
cockroach (Fig. 48, m. em). 

The cervical sclerites. — The cervical scler- 
ites are the small sclerites found in the neck of 
many insects. Of these there are dorsal, 
lateral, and ventral sclerites. The cervical 
sclerites were so named by Huxley ('78); 
Pig_ 50.— Head of a recently they have been termed the t7i/(?r5^g- 
cricket, ental surface mental plates by Crampton ('17), who con- 
wa . siders them to be homologous with sclerites 

found in the intersegmental regions of the 
thorax of some generalized insects. 

The lateral cervical sclerites have long been known as the jugular 
sclerites {pieces jugulaires, Straus Durckheim, 1828). 

C. THE APPENDAGES OF THE HEAD 

Under this category are classed a pair of jointed appendages 
termed the antennce, and the organs known collectively as the mouth- 
parts. 

The antemiae. — The antennae are a pair of jointed appendages 
articulated with the head in front of the eyes or between them. The 
antennse vary greatly in form; in some insects they are thread-like, 
consisting of a series of similar segments ; in others certain segments 
are greatly modified. The thread-like form is the more generalized. 

In descriptive works names have been given to particular parts of the antennae, 
as follows (Fig. 51): 

The Scape. — The first or proximal segment of an antenna is called the scape (a). 
The proximal end of this segment is often subglobose, appearing like a distinct 
segment; in such cases it is called the bulb (a'). 



THE EXTERNAL ANATOMY OF INSECTS 



41 



a- 




The Pedicel.— The. pedicel is the second segment of an antenna {b). In 
some insects it differs greatl}^ in form from the other segments. 

The Cldvola.— The term cla- 
y^ ,'-' '-.^ vola is applied to that part of 

;■ ^--'' """-,^ the antenna distad of the pedi- 

cel (c); in other words, to all 
of the antenna except the first 
and second segments. In some 
insects certain parts of the cla- 
vola are specialized and have 
received particular names. 
These are the ring- joints, the 
funicle, and the club. 

Tne Eing-joints. ^In certain 
Fig. 51.— Antennaofachalcis-fly. insects (e..?., Chalcididse) the 

proximal segment or segments of the clavola are much shorter than the suc- 
ceeding segments; in such cases they have received the name of ring-joints (c*). 

The Club.— In many insects the distal seg- 
ments of the antennas are more or less enlarged. 
In such cases they are termed the club (c^). 

The Funicle. — The funicle (c^) is that part 
of the clavola between the club and the ring- 
joints; or, when the latter are not specialized, 
between the club and the pedicel. 

The various forms of antenna; are designated 
by special terms. The more common of these 
forms are represented in Fig. 52. They are 
as follows: 

1. Setaceous or bristle-like, in which the 
segments are successively smaller and smaller, 
the whole organ tapering to a point. 

2. Filiform or thread-like, in which the 
segments are of nearly uniform thickness. 

3. Mbmliform or necklace-form, in which 
the segments are more or less globose, suggesting 
a string of beads. 

4. Serrate or saw-like, in which the segments 
are triangular and project like the teeth of a saw. 

5. Pectinate or comb-like, in which the seg- 
ments have long processes on one side, like the 
teeth of a comb. 

6. Clavile or club-shaped, in which the segments becon3 gradually broader, 
so that the whole organ assumes the form of a club. 

7. Capitate or with a head, in which the terminal segment or segments form 
a large knob. 

8. Lamellate in which the segments that compose the knob are extended on 
one side into broad plates. 

When an antenna is bent abruptly at an angle like a bent knee (Fig. 51) it is 
said to be geniculate. 




Fig. 52. — Various forms "of 
antennae. 



42 



AN INTRODUCTION TO ENTOMOLOGY 






The mouth-parts. — The mouth-parts consist typically of an uppe:.' 
lip, lahrum, an under lip, labium, and two pairs of jaws acting hori- 
zontally between them. The upper jaws are called the mandibles; 

the lower pair, the maxillos. 
The maxillae and labium are 
each furnished with a pair of 
feelers, called respectively 
the maxillary palpi, and 
the labial palpi. There 
may be also within the 
mouth one or two tongue- 
like organs, the epipharynx 
and the hypopharynx. The 
mouth-parts of a locust will 
serve as an example of the 
typical form of the mouth- 
parts (Fig. 53). 

The mouth-parts enumer- 
ated in the preceding paragraph 
are those commonly recognized 
in insects; but in certain insects 
there exist vestiges of a pair of 
lobes between the mandibles and 
the maxillae, these are the parag- 
natha. 

No set of organs in the 
body of an insect vary in 
form to a greater degree than 
do the mouth-parts. Thus 
with some the mouth is 
formed for chewing, while with others it is formed for sucking. 
Among the chewing insects some are predaceous, and have jaws fitted 
for seizing and tearing their prey; others feed upon vegetable matter, 
and have jaws for chewing this kind of food. Among the sucking 
insects the butterfly merely sips the nectar from flowers, while the 
mosquito needs a powerful instniment for piercing its victim. In 
this chapter the typical form of the mouth-parts as illustrated by the 
biting insects is described. The various modifications of it presented 
by the sucking insects are described later, in the discussions of the 
characters of those insects. 




Fig. 



53. — Mouth-parts of 
rum; md, mandible; mx, 
pharynx; /, labium. 



a locust: la, lab- 
maxilla; h, hypo- 



THE EXTERNAL ANATOMY OF INSECTS 



43 



The lahrum. — The Idbrum or upper lip (Fig. 53), is a more or less 
flap-like organ above the opening of the mouth. As it is often freely- 
movable, it has the appearance of an appendage of the body; but it 
is not a true appendage, being a part of one of the body segments that 
enter into the composition of the head. 

The mandibles. — The mandibles are the upper pair of jaws (Fig. 
53). They represent the appendages of one of the segments of the 
head. In most cases they are reduced to a single segment; but in 
some insects, as in certain beetles of the family Scarabceidae, each 
mandible consists of several more or less distinct sclerites. 

The pardgnatha. — In some insects there is between the mandibles 
and the maxillae a pair of more or less appendage-like organs borne by 
the hypopharynx. These are 
the "paraglossas" of writers on 
the Thysanura and Collembola 
and the "superhnguae" of Fol- 
som ('00). They were termed 
the maxillulae, a diminutive of 
maxillas by Hansen ('93), who 
regards them as homologous 
with the first maxillae of the 
Crustacea. But it has been 
shown by Cramp ton ('21) that 
they are homologous with the paragnatha of Crustacea. In 
Figure 54, A. represents a ventral view of the hypopharynx, parag- 
natha, and mandibles of the crustacean Ligyda; and B. the same 
parts of a naiad of a May-fly, Heptagenia. Paragnatha have been 
found in the Thysanura, Dermoptera, Orthoptera, Corrodentia, the 
naiads of Ephemerida, and the lar\^£e of Coleoptera. 

The MaxillcB. — The maxUlcB are the second pair of jaws of insects. 
Like the mandibles they are the appendages of one of the segments 
of the head. 




Fig. 54. — A. Posterior (ventral) view of 
mandibles and hypopharynx of the 
crustacean Ligyda; h, hypopharynx; 
p, paragnatha; m, mandibles; B. 
Same of a nymph of the Mayfly 
Heptagenia (From Crampton). 



The maxilte are much more complicated than the mandibles, each maxilla 
consisting, when all of the parts are present, of five primary parts and three 
appendages. The primary parts are the cardo or hin^e, the stipes for foot- 
stalk, the palpifer or palpus-bearer, the subgalea or helmet-bearer, and the 
lacinia or blade. The appendages are the maxillaiy palpus or feeler, the galea 



44 AN INTRODUCTION TO ENTOMOLOGY 

or superior lobe, and the digitus or finger. The maxilla may also bear claw-like 
or tooth-Hke projections, spines, bristles, and hairs. 

In the following description of the parts of the maxillae, only very general 
statements can be made. Not only is there an infinite variation in the form of 
these parts, but the same part may have a very different outline on the dorsal 
aspect of the maxilla from what it has on the ventral. Compare Fi . 55 and Fig. 
56, which represent the two aspects of the maxilla of Hydrophikis. Excepting 
Fig. 56, the figures of maxillas represent the ventral aspect of this organ. 

The cardo or hinge {a) is the first or proximal part of the maxilla. It is usually 
more or less triangular in outline, and is the part upon which nearly all of the 
motions of this organ depend In many cases, hov/ever, it is not th: only naxt 
directly joined to the body; for frequently muscles extend direct to '.e :b.";alea, 
without passing through the cardo. 

The stipes or footstaUc {h) is the part next in order proceeding distad. It is 
usually triangular, and articulates with the cardo by its base, with the palpifer 
by its lateral margin, and with the subgalea by its mesal side. In many insects 
the stipes is united with the subgalea, and the two form the larger portion of the 
body of the maxilla (Fig. 53). The stipes has no appendages; but the palipfer 
on the one side, and the subgalea on the other, may become united to the stipes 
without any trace of sutvire remaining, and their appendages will then appear 
to be borne by the stipes. Thus in Fig. 53 it appears to be the stipes that bears 
the galea, and that receives muscles from the body. 

The palpifer or palpus-bearer (c) is situated upon the lateral (outer) side 

of the stipes; it does not, 
however, extend to the base 
of this organ, and frequently 
projects distad beyond it. 
It is often much more 
developed on the dorsal 
side of the maxilla than on 
the ventral (Figs. 55 and 56). 
It can bereadily distinguished 
when it is distinct by the 

^. ,, , T>- ^ T^ 1 insertion upon it of the ap- 

Fig. 5S. — \entral as- Fig. 56. — Dorsal as- , t.- t, • ^ -4. 

pect of a maxilla of pect of a maxilla of Pondage which gives to it 

Hydrophilus. Hydrophilus. its name. 

The maxillary palpus or 
feeler {d) is the most conspicuous of the appendages of the maxilla. It is an 
organ composed of from one to six freely movable segments, and is articulated 
to the palpifer on the latero-distal angle of the body of the maxilla. 

The subgalea or heknet-bearer (e) when developed as a distinct sclerite is most 
easily distinguished as the one that bears the galea. It bounds the stipes more 
or less completely on its mesal (inner) side, and is often directly connected 
with the body by muscles. In many Coleoptera it is closely united to the 
lacinia; this gives the lacinia the appearance of bearing the galea, and of being 
connected with the body (Fig. 56). In several orders the subgalea is united to 
the stipes; consequently in these orders the stipes appears to bear the galea, 
and to be joined directly to the body if any part besides the cardo is so 
connected. 




THE EXTERNAL ANATOMY OF INSECTS 



45 




Fig- 57- — Maxilla oiCicindela. 



The galea or helmet (/) is the second in prominence of the appendages 

of the maxilla. It consists of one or two segments, and is joined to the maxilla 

^ mesad of the palpus. The galea varies greatly 

in form: it is often more or less flattened, with 

the distal segment concave, and overlapping 

the lacinia like a hood. It was this form that 

suggested the name galea or helmet. In other 

^-A>'*SJ ' \ 4 r^ t^^"^ cases the galea resembles a palpus in form (Fig. 

rX- \ \ \ V* r^~^ 57)- The galea is also known as the otiter lobe, 

'~'~^S\x^ ^^^"Z^ the upper lobe, or the superior lobe. 

The lacinia or blade (g) is borne on the mesal 
(inner) margin of the subgalea. It is the cutting 
or chewing part of the maxilla, and is often 
furnished with teeth and spines. The lacinia is 
also known as the inner lobe, or the inferior lobe. 

The digitus or finger {h) is a small appendage 
sometimes borne by the lacinia at its distal end. 
In the Cicindelidas it is in the form of an articu- 
lated claw (Fig. 57) ; but in certain other beetles 
it is more obviously one of the segments of the 
maxilla (Figs. 55 and 56). 

The labium or second maxillce. — The labium or under lip (Fig. 53), 
is attached to the cephaHc border of the gula, and is the most ventral 
of the mouth-parts. It appears to be a single organ, although some- 
times cleft at its distal extremity; it is, however, composed of a pair 
of appendages grown together on the middle line of the body. In the 
Crustacea the parts corresponding to the labiimi of insects consists of 
two distinct organs, 
resembling the 
maxillae; and in the 
embryos of insects 
the labium arises as 
a pair of append- 
ages. 

In naming the parts 
of the labium, entomo- 
logists have usually 
taken some form of it 
in which the two parts 
are completely grown 
together, that is, one 
which is not cleft on 
the middle line (Fig. 

58). I will first describe such a labium, and later one 
into two parts is carried as far as we find it in insects. 




Fig. 58. — Labium of Harpalus. 

in which the division 






^£4^^ 



LISRARY 



V! 



%^ 



46 AN INTRODUCTION TO ENTOMOLOGY 

The labium is usually described as consisting of three principal parts and a 
oair of appendages. The principal parts are the sv.b'r.icvAv.m, the mentum, and 
the Ugida; the appendages are the labial palpi. 

The submentum. The basal part of the labium consists of Lwo transverse 
sclerites; the proximal one, which is attached to the cephalic border ol the gula, 
is the submetitutn (a). This is often the most prominent part of the body of 
the labium. 

The mentum is the more distal of the two primary parts of the labium (b). 
It is articulated to the cephahc border of the submentum, and is often so 
slightly developed that it is concealed by the submentum. 

The ligula includes the remaining parts of the labium except the labial palpi. 
It is a compound organ; but in the higher insects the sutures between the 
different sclerites of which it is composed are usually obsolete. Three parts, 
however, are commonly distinguished (Fig. 58), a central part, often greatly 
prolonged, the glossa (c^) and two parts, usually small membranous projections, 
one on each side of the base of the glossa, the paraglossce (c^) . Sometimes, how- 
ever, the paraglossas are large, exceeding the glossa in size. 

The labial palpi. From the base of the ligula arise a pair of appendages, the 
labial palpi. Each labial palpus consists of from one to four freely movable 
segments. 

In the forms of the labium just described, the correspondence of its parts to 
the parts of the maxillae is not easily seen; but this is much more evident in the 
labium of some of the lower insects, as for example a cockroach (Fig. 59). Here 
the organ is very deeply cleft; only the submentum 
and mentum remain united on the median line; while 
the ligula consists of two distinct maxilla-like parts. 
It is easy in this case to trace the correspondence 
referred to above. Each lateral hr.lf of the submentum 
corresponds to the cardo of a maxilla; each half of the 
mentum, to the stipes; while the remaining parts of a 
maxilla are represented by each half of the ligula, as 
follows: near th base of the ligula there is a part (c') 
which bears the labial palpus; this appears in the 
figure like a basal segment of the palpus; but in many 
msects it is easily seen that it is undoubtc '.ly one of 
the primary parts of the organ; it has been named 

Pig, gg, Labium of a ^^^^ palpiger, and is the homologue of the palpifer of 

cockroach. a maxilla. The trunk of each half of the ligula is 

formed by a large sclerite (c*) ; this evidently corres- 
ponds to the subgalea. At the distal extremity of this subgalea of the labium 
there are two appendages. The lateral one of these (c^) is the paraglossa. 
and obviously corresponds to the galea. The mesal one (c^) corresponds to the 
lacinia or inner lobe. This part is probably wanting in those insects in which 
the glossa consists of an undivided part; and in this case the glossa probably 
represents the united and more or less elongated subgaleag. 

The epipharynx. — In some insects there is borne on the ental sur- 
face of the labtum, within the cavity of the mouth, an unpaired fold, 
which is membranous and more or less chitinized' this is the epi- 
phdrynx. 




THE EXTERNAL A NA TOMY OF INSECTS 47 

The hypopharynx. — The hypophdrynx is usually a tongue-like 
organ borne on the floor of the mouth cavity. This more simple form 
of it is well-shown in the Orthoptera (Fig. 53). To the hypopharnyx 
are articulated the paragnatha when they are present. The hypo- 
pharynx is termed the lingua by some writers. 

d. THE SEGMENTS OF THE HEAD 

The determination of the number of segments in the head of an insect is a 
problem that has been much discussed since the early days of entomology. The 
first important step towards its solution was made by Savigny (18 16), who sug- 
gested that the movable appendages of the head were homodyanmous with legs. 
This conclusion has been accepted by all ; and as each segment in the body of an 
insect bears only a single pair of appendages, there are at least four segments 
in the head; i. e., the antennal, the mandibular, the maxillary, and the second 
maxillary or labial. 

In more recent times workers on the embryology of insects have demonstrated 
the presence of two additional segments. First, there has been found in the 
embryos of many insects a pair of evanescent appendages situated between the 
antennse and the mandibles. These evidently correspond to the second antennee 
of Crustacea, and indicate the presence of a second antennal segment in the head 
of an insect. This conclusion is confirmed by a study of the development of the 
nervous system. And in the Thysanura and CoUembola vestiges of the second 
a.ntennas persist in the adults of certain members of these orders. 

Second, as the compound eyes are borne on movable stalks in certain Crusta- 
cea, it was held by Milne-Edwards that they represent another pair of appendages; 
but this view has not been generally accepted. It is not necessary, however, to 
discuss whether the eyes represent appendages or not ; the existence of an ocular 
segment has been demonstrated by a study of the development of the nervous 
system. 

It has been shown that the brain of an insect is formed from three pairs of 
primary ganglia, which correspond to the three principal divisions of the brain, 
the protecerebrum, the deutocerebrum, and the tritocerebrum . And it has also been 
shown that the protocerebrum innervates the compound eyes and ocelli; the 
deutocerebrum, the antenns; and the tritocerebrum, the labrum. This demon- 
strates the existence of three premandibular segments: an ocular segment or 
protocerebral segment, without appendages, unless the compound eyes repre- 
sent them; an antennal or deutocerebral segment, bearing antennae; and a 
second antennal or tritocerebral segment, of which the labrum is a part, and to 
which the evanescent appendages between the antennse and the mandibles doubt- 
less belong. As Viallanes has shown that the tritocerebrum of Crustacea inner- 
vates the second antennae, we are warranted in considering the tritocerebral 
segment of insects to be the second antennal segment. 

Folsom ('00) in his work on the development of the mouth-parts of Anurida 
described a pair of primary ganglia which he believed indicated the presence of a 
segment between the mandibular and maxillary segments. He named the ap- 
pendages of this segment the superlingucc; they are the paragnatha described above. 

The existence of the supposed ganglia indicating the presence of a super- 
lingual segment has not been confirmed by other investigators and is no longer 
maintained by Folsom. 



48 



AN INTRODUCTION TO ENTOMOLOGY 



The suboesophageal ganglion is formed by the union of three pairs of primitive 
ganglia, pertaining respectively to the mandibular, the maxillary, and the labial 
segments of the embryo. 

LIST OF THE SEGMENTS OF THE HEAD 

First, ocular, or protocerebral. 

Second, antennal, or deutocerebral. 

Third, second antennal, or tritocerebral. 

Fourth, mandibular. 

Fifth, maxillary. 

Sixth, labial, or second maxillary. 



III. THE THORAX 



a. THE SEGMENTS OF THE THORAX 

The prothorax, the mesothorax, and the metathorax. — The thorax 
is the second or intermediate region of the body ; it is the region that 
in nymphs, naiads, and adults bears the organs of locomotion, the legs, 
and the wings when they are present. This region is composed of 
three of the body-segments more or less firmly joined together; the 
segments are most readily distinguished by the 
fact that each bears a pair of legs. In winged 
insects, the wings are borne by the second and 
third segments. The first segment of the thorax, 
the one next the head, is named the prothorax; 
the second thoracic segment is the mesothorax; 
and the third, the metathorax. 

The simplest form of the thorax in adult 
insects occurs in the Apterygota (the Thysanura 
and the Collembola) where although the seg- 
ments differ in size and proportions, they are 
distinct and quite similar (Fig. 60). 

In the Pterygota, or winged insects, the 
prothorax is either free or closely united to the 
mesothorax ; in many cases it is greatly reduced in 
size; it bears the first pair of legs. The meso- 
thorax and the metathorax are more or less closely 
united, forming a box, which bears the wings and 
the second and third pairs of legs. This union of 
these two segments is often so close that it is very difficult to distin- 
guish their limits. Sometimes the matter is farther complicated by 
a union with the thorax of a part or of the whole of the first 




Pig. 60. — Lepisma 
saccharina (After 
Lubbock). 



THE EXTERNAL ANATOMY OF INSECTS 49 

abdominal segment. In the Acridiidae, for example, the sternum of 
the first abdominal segment forms a part of the intermediate region 
of the body, and in the Hymenoptera the entire first abdominal 
segment pertains to this region. 

The alitrunk. — ^When, as in the Hymenoptera, the intermediate 
region of the body includes more than the three true thoracic seg- 
ments it is designated the dlitrnnk. 

The propodeum or the median segment. — ^When the alitrunk con- 
sists of four segments the abdominal segment that f omis a part of it is 
teniied the propodeum or the median segment. In such cases the true 
second abdominal segment is termed the first. 

h. THE SCLERITES OF A THORACIC SEGMENT 

The parts of the thorax most generally recognized by entomologists 
were described nearly a century ago by Audouin (1824) ; some addi- 
tional parts not observed by Audouin have been described in recent 
times, by the writer ('02), Verhoeff ('03), Crampton ('og), and 
Snodgrass ('09, '10 a, and '10 h). The following account is based on 
all of these works. 

In designating the parts of the thorax the prefixes pro, meso, and 
meta are used for designating the three thoracic segments or corres- 
ponding parts of them; and the prefixes pre and post are used to 
designate parts of any one of the segments. Thus the scutum of the 
prothorax is designated the proscutum; while the term prescutum is 
applied to the sclerite immediately in front of the scutum in each of 
the thoracic segments. This system leads to the UL^e of a number of 
hybrid combinations of Latin and Greek terms, but it is so firmly 
established that it would not be Vv^ise to attempt to change it on this 
account. 

Reference has already been made to the division of a body-segment 
into a tergum, two pleura, and a sterntun ; each of these divisions will 
be considered separately; and as the maximum number of parts are 
found in the wing-bearing segments, one of these will be taken as an 
illustration. 

The sclerites of a tergum. — In this discussion of the external ana- 
tomy of the thorax reference is made only to those parts that form 
the external covering of this region of the body. The infoldings of 
the body- wall that constitute the internal skeleton are discussed in the 
next chapter. 

The notum. — In nymphs and in the adults of certain generalized 
insects the tergum of each wing-bearing segment contains a single 



50 



AN INTRODUCTION TO ENTOMOLOGY 



chitinized plate; this sclerite is designated the notum. The term 
notum is also applied to the tergal plate of the prothorax and to that 
of each abdominal segment. The three thoracic nota are designated 
as the pronotum, the mesonotum, and the metanotum respectively. 

The notum of a wing-bearing segment is the part that bears the 
wings of that segment, even when the tergum contains more than one 
sclerite. Each wing is attached to two processes of the notum, the 
anterior notal process (Fig. 6i, a n p) and the posterior notal process 
(Fig. 61, p n p); and the posterior angles of the notum are produced 
into the axillary cords, which form the posterior margins of the basal 
membranes of the wings. 

The postnotmn or postscutellum. — In the wing-bearing segments of 
most adult insects the tergum consists of two principal sclerites ; the 
notum already described, and behind this a narrower, transverse 
sclerite which is commonly known as the postscutellum, and to which 
Snodgrass has applied the term postnotum (Fig. 61, P N). 

The divisions of the notum. — In most specialized insects the notum 
of each wing-bearing segment is more or less distinctly divided by 
transverse lines or sutures into three parts; these are known as the 
prescUtum (Fig. 61, Psc), the scutum (Fig. 61, Set), and the scutellum 
(Fig. 61, Scl). 

It has been commonly held, since the 
days of Audouin, that "the tergum of each 
thoracic segment is composed typically of four 

sclerites, the prescutum, scutum, scutellum, , -^^-> 

and postscutellum. But the investigations of 
Snodgrass indicate that in its more genera- 
lized form the tergum contains a single ^" 
sclerite, the notum; that the postscutellum ^^ 
or postnotum is a secondary tergal chitini- 
zation in the dorsal membrane behind the j^- 
notum, in more specialized insects; and that £p^ 
the separation of the notum into three parts, 
the prescutum, scutimi, and scutellum, is a 
still later specialization that has arisen 
independently in different orders, and does 
not indicate a division into homologous 
parts in all orders where it exists. 

The patagia. — In many of the more 
specialized Lepidoptera the pronotum Fig. 61. — Diagram of a generalized 
is produced on each side into a flat thoracic segment (From Snod- 
1 u t,- 1, • • grass), 

lobe, which m some cases is even con- 
stricted at the base so as to become a stalked plate, these lobes are 
the patagia. 




THE EXTERNAL ANATOMY OF INSECTS 



51 



The parapsides. — In some Hymenoptera the scutum of the meso- 
thorax is divided into two parts by the prescutum; these separated 
halves of the scutum are called the parapsides (see Fig. 1 130A). 

The sclerites of the pleura. — In the accompanying figure (Fig. 61) 
the sclerites of the left pleunim of a wing-bearing segment are repre- 
sented diagrammatically ; these sclerites are the following: 

The episternum. — Each pleurum is composed chiefly of two 
sclerites, which typically occupy a nearly vertical position, but 
usually are more or less oblique. In most insects the dorsal end of 
these sclerites extends farther forward than the ventral end, but in 
the Odonata the reverse may be true. The more anterior in position 
of these two sclerites is the episternum (Fig. 61, Eps). 

In several of the orders of insects one or more of the episterna are 
divided by a distinct suture into an upper and a lower part. These 
two parts have been designated by Crampton ('09) as the anepister- 
num and the katepisternum respectively (Fig. 62). 

The epimerum. — The epimerum is the more posterior of the two 
principal sclerites of a pleurum (Fig. 61). It is separated from the 
episternum by the pleural suture (Fig. 61, PS) which extends from the 
pleural wing process above (Fig. 61, Wp) to the pleural coxal process 
below (Fig. 61, CxP). 

In some of the orders of insects one or more of the epimera are 
divided by a distinct suture into an upper and a 
lower part. These two parts have been desig- 
nated by Crampton ('09) as the anepimerum 
and the katepimeruni respectively (Fig. 62). 

The preepisternum. — In some of the more 
generalized insects there is a sclerite situated 
in front of the episternum; this is the pre- 
episternum. 

The paraptera. — In many insects there is on 
each side a small sclerite between the upper 
end of the episternum and the base of the wing ; 
these have long been known as the paraptera. 
Snodgrass (10 o) has shown that there are in 
some insects two sclerites in this region, which, 
he designates the episternal paraptera. or 
preparaptera (Fig. 61, iP and 2P); and that 
one or occasionally two are similarly situated 
between the epimerum and the base of the wing, 
the epimeral paraptera or postparaptera (Fig. 61, 3P). 




Fig. 62. — Lateral aspect 
of the meso- and meta- 
thorax of Mantis pa 
rugicollis; i, i, anepis- 
ternum ;2, 2, katepister- 
num; 3,3, anepimer- 
um; 4,4,katepimerum; 
c, c, coxa. 



52 



AN INTRODUCTION TO ENTOMOLOGY 



The spiracles. — The external openings of the respiratory system 
are termed spiracles. Of these there are two pairs in the thorax. 
The first pair of thoracic spiracles open, typically, one on each side in 
the transverse conjunctiva between the prothorax and the meso- 
thorax ; the second pair open in similar positions between the meso- 
thorax and the me athorax. In some cases the spiracles have 
migrated either fonvard or backward upon the adjacent segment. 
For a discussion of the number and distribution of the spiracles, see 
the next chapter. 

The periiremes. — In many cases a spiracle is surrounded by a cir- 
cular sclerite; such a sclerite is termed a peritreme. 

The acelabula or coxal cavities. — In some of the m.ore specialized 
insects, as many beetles for example, the basal segment of the legs is 
inserted in a distinct cavity ; such a cavity is termed an aceidbuhtfn or 
^uxal cavity. When the epimera of the prothorax extend behind the 
coxae and reach the prostemum, the coxal cavities are said to be 
closed (Fig. 63) ; when the epimera do not extend behind the coxa 
to the prosterum, the coxal cavities are described as open (Fig. 54) . 

The sclerites of a sternum. — In the more generalized insects the 
sternimi of a wing-bearing segment may consist of three or four 
sclerites. These have been designated, beginning with the anterior 
one, the presternum (Fig. 
61, Ps), the sternum or 
eusternum (Fig. 61, 5), 
the sternellum (Fig. 61, 
SI) , and the postsiernellum. 
(Fig. 61, Pst). 

In the more special- 
ized insects only one of 
these, the sternum, re- 
mains distinctly visible. 
It is an interesting fact 
that while in the speciali- 
zation of tue tergum 
there is an increase in 
the nimiber of the scleri- 
tes in this division of a 
segment, in the specialization of the sternimi there is a reduction. 

It is a somewhat unfortunate fact that the term sternum has been 
used in two senses : first, it is applied to the entire ventral division of 
a segment ; and second, it is applied to one of the sclerites entering 




Fig. 63. — Prothorax of Harpa.,is, ventral aspect; 
c, coxa; em, epimerum; is, episternum; /, 
femur; n, pronotum; s, s, s, prostemum. 



THE EXTERNAL ANATOMY OF INSECTS 



53 




Fig. 64. — Prothorax of Penlhe; c, coxa; cc, coxal 
cavity ;/, femur ; 5, prosternum; </-, trochanter. 



into the composition of this division when it consists of more than 
a single sclerite. To meet this difficulty Snodgrass has proposed 

that the term eusternum 
be applied to the sclerite 
that has been known as 
the sterntun; and that 
the word sternum be 
used only to designate 
the entire ventral divi- 
sion of a segment. 

C. THE ARTICULAR 

SCLERITES OF THE 

APPENDAGES 

Atthebaseofeachleg 
and of each wing there 
are typically several 
sclerites between the appendage proper and the sclerites of the trunk 
of the segment ; these sclerites, which occupy an intermediate position 
between the body and its appendage, are termed the articular sclerites. 

Frequently one or more of the articular sclerites become consoli- 
dated with sclerites of the trunlc so as to appear to form a part of its 
wall; this is especially true of those at the base of the legs. 

The articular sclerites of the legs. — ^The proximal segment of the leg, 
the coxa, articulates with the body by means of two distinct articula- 
tions, which may be termed the pleural articulation of the coxa and the 
ventral articulation of the coxa respectively. The pleural articulation 
is with the ventral end of the foot of the lateral apodeme of the seg- 
ment, i. e. with the pleural coxal process, which is at 
the ventral end of the suture between the epistemum 
and the epimerum (Fig. 61, CxP). The ventral arti- 
culation is with a sclerite situated between the coxa 
and the episternum; this sclerite and others asso- 
ciated with it may be termed the articular sclerites 
of the legs. The articular sclerites of the legs to 
which distinctive names have been applied are the 
following : 

The trochantin. — The maximum number of 
articular sclerites of the legs are found in the more 
generalized insects; in the more specialized insects 
the number is reduced by a consolidation of some of them with 




Fig. 65.— The 
base of a leg 
of a cock- 
roach. 



54 AN INTRODUCTION TO ENTOMOLOGY 

adjacent parts. The condition found in a cockroach may be taken 
as typical. In this insect the trcchdntin (Fig, 65, t) is a triangular 
sclerite, the apex of which points towards the middle line of the body, 
and is near the ventral articulation of the coxa (Fig. 6s,y). In most 
specialized insects the trochantin is consolidated with the antecoxal 
piece, and the combined sclerites, which appear as one, are termed 
the trochantin. 

The antecoxal piece. — Between the trochantin and the epistemum 
there are, in the cockroach studied, two sclerites; the one next the 
trochantin is the antecoxal -piece. This is the articular sclerite that 
articulates directly with the coxa (Fig. 65, ac). As stated above, the 
antecoxal piece is usually consolidated with the trochantin, and the 
term trochantin is applied to the combined sclerites. Using the term 
trochantin in this sense, the statement commonly made that the 
ventral articulation of the coxa is with the trochantin is true. 

The second anteccxal piece. — The sclerite situated between the 
antecoxal piece and the epistemtmi is the second antecoxal piece (Fig. 
65, 2 ac). This is quite distinct in certain generalized insects; but it 
is usually lacking as a distinct sclerite. 

The articular sclerites of the wings. — In the Ephemerida and Odo- 
nata the chitinous wing -base is directly continuous with the walls of 
the thorax. In all other orders there are at the base of each wing 
several sclerites which enter into the composition of the joint by which 
the wing is articulated to the thorax ; these may be termed collectively 
the articular sclentes of the uy>ngs. Beginning with the front edge 
of this joint and passing backward these sclerites are as follows: 

The iegula. — In several orders of insects there is at the base of the 
costal vein a small, hairy, slightly chitinized pad; this is the tegula 
(Fig. 66, Tg). In the more highly specialized orders, the Lepidoptera, 
the Hymenoptera, and the Diptera, the tegula is largely developed 
so as to form a scale-like plate overlapping the base of the wing. 

The tegulag of the front wings of Lepidoptera are specially large 
and are carried by special tegular plates of the notum. These, in turn, 
are supported by special internal tegular arms from the bases of the 
pleural wing -processes (Snodgrass, '09) 

The axillaries. — Excepting the tegula, which is at the front edg3 
of the wing-joint, the articular sclerites of the wings have been termed 
collectively the axillaries. Much has been written about these 
sclerites, and many names have been applied to them. The simplest 
terminology is that of Snodgrass ('09 and '10 a) which I here adopt. 



THE EXTERNAL ANATOMY OF INSECTS 



55 



The first axillary. — This sclerite (Fig. 66, i Ax) articulates with 
the anterior notal wing-process and is specially connected with the 
base of the subcostal vein of the wing. In rare cases it is divided 
into two. 

The second axillary. — The second axillary (Fig. 66, 2 Ax) articulates 
with the first axillary proximally and usually with the base. of the 
radius distally; it also articulates below with the wing-process of the 
pleurum, constituting thus a sort of pivotal element. 

The third axillary. — The third axillary (Fig. 66, 3 Ax) is interposed 
between the bases of the anal veins and the fourth axillary when this 
sclerite is present. When the fourth axillary is absent, as it is in 




Fig. 66. — Diagram of a generalized wing and its articular sclerites (From 
Snodgrass). 

nearly all insects except Orthoptera and Hymenoptera, the third 
axillary articulates directly with the posterior notal wing-process. 

The fourth axillary. — When this sclerite is present it articulates 
with the posterior notal wing-process proximally and with the third 
axillary distally (Fig. 66, 4 Ax). Usually this sclerite is absent; it 
occurs principally in Orthoptera and Hymenoptera. 

The median plates. — The median plates of the wing-joint are not 
of constant shape and occurrence; when present, these plates are 
associated with the bases of the media, the cubitus, and the first anal 
vein when the latter is separated from the other anals. Often one of 
them is fused with the third axillary and sometimes none of them^ are 
present. 



THE APPENDAGES OF THE THORAX 



The appendages of the thorax are the organs of locomotion. 
They consist of the legs and the u ings. Of the former there are three 



56 



AN INTRODUCTION TO ENTOMOLOGY 



pairs, a pair borne by each of the three thoracic segments; of the 
latter there are never more than two pairs, a pair borne by the meso- 
thorax and a pair borne by the metathorax. One or both pairs of 
wings may be wanting. 

The legs. — Each leg consists of the following named parts and 
their appendages: coxa, trochanter, femur, tibia, and tarsus. 

The coxa. — The coxa is the proximal segment of the leg; it is the 
one by which the leg is articulated to the body (Fig. 67). The coxa 
varies much in form, but it is usually a truncated cone or nearly 
globular. In some insects the coxae of the third pair of legs are more 
or less flattened and immovably attached to the metasternum; this 
is the case in beetles of the family Carabidas for example. In such 
cases the coxas really form a part of the body-wall, and are liable to be 
mistaken for primary parts of the metathorax instead of the proximal 
segments of appendages. 

In several of the orders of insects the coxa is apparently composed 

of two, more 
or less dis- 
tinct, parallel 
parts; this is 
the case, for 
example, inin- 
sects of the 
trichopterous 
genus Neuro- 
ma (Fig. 68, 
Cx and epm). 
But it has 
been shown 
by Snodgrass 
('09) that the 
posterior part 
of the sup- 
posed double 
coxa, the 
"meron"(Fig. 
68, epm) is a 
detached por- 
tion of the 
epimerimi. 
The styli. — In certain generalized insects, as Machilis of the order 




Fig. 67. — Legs of insects: A, wasp; B, ichneumon-fly; C, 
bee; c, coxa; tr, trochanter; /, femur; ti, tibia; to, 
tarsus; m, metatarsus. 



THE EXTERNAL ANATOMY OF INSECTS 



57 



Thysanura, the coxa of each middle and hind leg bears a small 
appendage, the stylus (Fig. 69). The styli are of great interest as 
they are believed to correspond to one of the two branches of the legs 
of Crustacea; thus indicating that insects have descended from 
forms in which the legs were biramous. 

In several genera of the Thysanura one or more of the abdominal 
segments bear each a pair of styli ; in Machilis they are found on the 
second to the ninth abdominal segments. These styli are regarded as 
vestiges of abdominal legs. 

The trochanter. — The trochanter is the second part of the leg. It 
consists usually of a very short, triangular or quadrangular segment, 
between the coxa and the femur. Sometimes the femur appears to 
articulate directly with the coxa ; and the trochanter to be merely an 
appendage of the prox'mal end of the femur {e. g. Carabidas). But 
the fact is that in these insects, although the femur may touch the 
coxa, it does not articulate with it; and the 
organs that pass from the cavity of the coxa 
to that of the femur must pass through the 
trochanter. In some Hymenoptera the tro- 
chanter consists of two segments (67, B). 

The femur. — The femur is the third part of 
the leg; and is usually the largest part. It 
consists of a single segment. 

The tibia. — The tibia is the fourth part of 
the leg. It consists of a single segment; and 
Fig. 68.— Lateral aspect ^^ usually a little more slender than the femur, 
of the mesothorax of although it often equals or exceeds it in length. 
In such species as burrow in the ground, the 
distal extremity is greatly broadened and 
shaped more or less like a hand. Near the distal end of the tibia 
there are in most insects one or more spurs, which are much larger 
than the hairs and spines which arm the 
leg; these are called the tibial spurs, and 
are much used in classification. 

The tarsus. — The tarsus is the fifth and 
most distal part of the leg, that which is 
popularly called the foot. It consists of a 
series of segments, var^dng in number 
from one to six. The most common num- 
ber of segments in the tarsus is five. 

In many insects, the first segment of the tarsus is much longer, 




Neuronia (From Snod- 
grass). 




Fig. 69. — A leg of Machilis; 
s, stylus. 



58 AN INTRODUCTION TO ENTOMOLOGY 

and sometimes much broader, than the other segments. In such 
cases this segment is frequently designated as the metatarsus (Fig. 
67, C, m). 

In some insects the claws borne by the distal end of the tarsus are 
outgrowths of a small terminal portion of the leg, the sixth segment 
of the tarsus of some authors. This terminal part with its appendages 
has received the name prcetarsus (De Meijere '01). As a rule the 
prsetarsus is withdrawn into the fifth segment of the tarsus or is not 
piesent as a distinct segment. 

On the ventral surface of the segments of the tarsus in many 
insects are cushion-like structures; these are called pulvUli. The 
cuticula of the pulvilli is traversed by nvimerous pores which open 
either at the surface of the cuticula or through hollow hairs, the 
tenent-hairs, and from which exudes an adhesive fluid that enables the 
insect to walk on the lower surface of objects. 

With many insects (e. g. most Diptera) the distal segment of the 
tarsus bears a pair of pulvilli, one beneath each claw. In such cases 
there is frequently between these pulvilli a third single appendage of 
similar structure; this is called the empoiium; writers on the Orthop- 
tera commonly called the appendage between the claws the arolium. 
In other insects the empodium is bristle-like or altogether wanting. 

In many insects the pulvillus of the distal segment of the tarsus 
is a circular pad projecting between the tarsal claws. In many 
descriptive works this is referred to as the pulvillus , even though the 
other pulvilli are well-developed. The pulvilli are called the onychii 
by some writers. 

The claws borne at the tip of the tarsus are termed the tarsal claws 
or ungues; they vary much in form; they are usually two in nimiber, 
but sometimes there is only one on each tarsus. 

The wings. — The wings of insects are typically two pairs of mem- 
branous appendages, one pair borne by the mesothorax and one pair 
by the metathorax; prothoracic wings are unknown in living insects 
but they existed in certain paleozoic forms. 

Excepting in the subclass Apterygota which includes the 
orders Thysanura and Collembola, wings are usually present in adult 
insects. Their absence in the Apterygota is due to the fact that 
they have not been evolved in this division of the class Hexapoda; 
but when they are absent in adult members of the subclass Pterygo- 
ta, which includes the other orders of insects, their absence is due 
to a degradation, which has resulted in their loss. 



THE EXTERNAL ANATOMY OF INSECTS 59 

The loss of wings is often confined to one sex of a species; thus 
with the canker-worm moths, for example, the females are wingless, 
while the males have well-developed wings; on the other hand, with 
the fig-insects, Blastophaga, the female is winged and the male 
wingless. 

Studies of the development of wings have shown that each wing is 
a saclike fold of the body-wall; but in the fully developed wing, its 
saclike nature is not obvious; the upper and lower walls become 
closely applied throughout the greater part of their extent ; and since 
they become very thin, they present the appearance of a single delicate 
membrane. Along certain lines, however, the walls remain separate, 
and are thickened, forming the firmer framework of the wing. These 
thickened and hollow lines are termed the veins of the wing ; and their 
arrangement is described as the venation of the wing. 

The thin spaces of the wings which are bounded by veins are 
called cells. When a cell is completely surrounded by veins it is said 
to be closed; and when it extends to the margin of the wing it is said 
to be open. 

The different types of insect wings. — What may be regarded as the 
typical form of insect wing is a nearly flat, deHcate, membranous 
appendage of the body, which is stiffened by the so-called wing-veins ; 
but striking modifications of this form exist; and to certain of them 
distinctive names have been applied, as follows: 

In the Coleoptera and in the Dermaptera, the front wings are 

thickened and ser^'e chiefly to protect the dorsal wall of the body and 

the membranous hind wings, which are folded beneath them when 

not in use. Front wings of this type are termed wing-covers or elytra. 

The front wings of the Hemiptera, which are thickened at the 

base like elytra, are often desig- 
nated the hemelytra. 

The thickened fore wings of 
Orthoptera are termed tegmina by 
many writers. 

The hind wings of Diptera, 
which are knobbed, thread-like 
organs, are termed haltcres. The 
hind wings of the males of the 
family Coccidse are also thread- 
Fig. 70. — Diasrram of a wing showing like, 
margins and angk^s. ,^1 -, -, ^ 

The reduced front wmgs of the 

Strepsiptera are known as the pseudo-halteres. 




60 



AN INTRODUCTION TO ENTOMOLOGY 



The margivs of wings. — -Most insect wings are more or less 
triangular in outline; they, therefore, present three margins: the 
costal margin or costa (Fig. 70, a-h)\ the outer margin (Fig. 70, 
h-c)\ and the inner margin (Fig. 70, c-d). 

The angles of wings. — The angle at the base of the costal margin 
of a wing is the humeral angle (Fig. 70, a) ; that between the costal 
margin and the outer margin is the apex of the wing (Fig. 70, h)\ 




2dA*Cu, 

Fig. 71. — Wing of Conops; ac, axillary excision; /, posterior lobe. 

and that between the outer margin and the inner margin is the anal 
a?gle (Fig. 70, c). 

The axillary cord. — The posterior margin of the membrane at the 
base of the wing is usually thickened and corrugated; this cord-like 
structure is termed the axillary cord. The axillary cord normally 
arises, on each side, from the posterior lateral angle of the notum, and 
thus serves as a mark for determining the posterior limits of the 

notum. 

The axillary membrane. — The 
membrane of the wing base is 
termed the axillary membrane; 
it extends from the tegula at the 
base of the costal margin to the 
axillary cord ; in it are found the 
axillary sclerites. 

The alula. — In certain families 
of the Diptera and of the Coleop- 
tera the axillary membrane is 
expanded so as to form a lobe or 
lobes which fold beneath the base of the wing when the wings are 
closed; this part of the wing is the alula or alulet. The alulas are 
termed the sgi^amcB by some writers, and the calypteres by others. 




Fig. 72. — Wings of the honeybee; 
A, hamuli. 



THE EXTERNAL ANATOMY OF INSECTS 



61 



The axillary excision. — In the wings of most Diptera and in the 
wings of many other insects there is a notch in the inner margin of 
the wing near its base (Fig. 71, ae), this is the axillary excision. 

The posterior lobe of the wing. — That part of the wing lying between 
the axillary excision when it exists, and the axillary membrane is the 
posterior lobe of the wing. The posterior lobe of the wing and an alula 
are easily differentiated as the alula is margined by the axillary cord. 

The methods of uniting the two wings of each side. — It is obvious 
that a provision for ensuring the synchronous action of the fore and 
hind wings adds to their efficiency; it is as important that the two 
pairs of wings should act as a unit as it is that the members of a boat's 
crew should pull together. In many insects the synchronous action 
of the wings is ensured by the fore wing overlapping the hind wing. 
But in other insects special structures have been developed which 
fasten together the two wings of each side. The different types of 
these structures have received special names as follows: 

The hamuli. — With certain insects the costal margin of the hind 
wings bears a row of hooks, which fasten into a fold on the inner 
margin of the fore wings (Fig. 72) ; these hooks are named the hamuli. 

The frenulum and the frenulum hook. — In most moths there is a 
strong spine-like organ or a 
bunch of bristles borne by the 
hind wing at the humeral 
angle (Fig. 73,/); this is the 
frenulum or little bridle. As a 
rule the frenulum of the female 
consists of several bristles ; that 
of the male, of a single, strong, 
spine-like organ. In the males 
of certain moths, where the 
frenulimi is highly developed, 
there is a membranous fold on 
the fore wing for recei\-ing the 
end of the frenulum, this is the 
frenulum hook (Fig. ^Sffh). 

The jugum. — In one family 
of moths, the Hepialidse, the 
posterior lobe of the fore wing 
is a slender, finger-like organ 
which is stiffened by a branch 
of the third anal vein, and which projects beneath the costal margin 
of the hind wing. As the greater part of the inner margin of the fore 




Fig- 73- — Wings of Thyridnpteryx ephemercB- 
formis; f, frpnulum; fh, frenulum hook. 



62 



AN INTRODUCTION TO ENTOMOLOGY 



wing overlaps the hind wing, the hind wing is held between the two 
(Fig. 74). This type of the posterior lobe of the fore wing is termed 
the jugum or yoke. The structure of the jugum is shown in Figure 75. 
The fibula. — In several groups of insects an organ has been 
developed that serves to unite the fore and hind wings, but which 
functions in a way quite different from that of the jugum. Like the 
jugum it is f oimd at the base of the fore wing ; but unlike the jugum 
it extends back above the base of the hind wing and is clasped over an 
elevated part of the hind wing; this organ is the fibula or clasp. 
In some insects, as in the Trichoptera, the fibula consists only of 
a specialized posterior lobe of the fore wing; in others, as in the 
genus Corydalns of the order Neuroptera, the proximal part of the 
fibula is margined by the axillary cord, showing that the axillary 
membrane enters into the composition of this organ (Fig. 76). 

The hypothetical type of the primitive wing-venation. — A careful 
study of the wings of many insects has shown that the fundamental 
type of venation is the same in all of the orders of winged insects. 
But this fact is evident only when the more primitive or generalized 
members of different orders are compared with each other. In most 
of the orders of insects the greater number of species have become so 

modified or specialized as 
regards the structure of 
their wings that it is diffi- 
cult at first to trace out the 
primitive type. 

This agreement in the 
important features of the 
venation of the wings of 
the generalized members of 
the different orders of insects 
is still more evident when 
the wings of nymphs, naiads, 
and pupae are studied. It 
has been demonstrated that 
in the development of wings 
of generalized insects the 
longitudinal wing-veins are 
formed about preexisting 
tracheae. In the develop- 
ment of the wing, these 
tracheee grow out into the 
wing-bud, and later the wing-veins are formed about them. 




Fig. 74. — Wings of a hepialid, seen from 
below; a, accessory vein. 



THE EXTERNAL ANATOMY OF INSECTS 



63 



The wings of nymphs, naiads, and pupae are broad at the base, 
and consequently the tracheag that precede the wing-veins are not 
crowded together as are the wing-veins at the base of the wings of 




Fig- 75- — Jugum of a hepialid 



Fibula of Corydalus. 



adults. For this reason the identity of the wing- veins can be deter- 
mined more surely in the wings of immature insects than they can be 
in the wings of adults. This is especially true where two or more 
veins coalesce in the adult wing while the tracheag that precede these 
veins are distinctly separate in the immature wing. 

A study was made of the tracheation of the wings of immature 
insects of representatives of most of the orders of insects, and, assum- 
ing that those features that are possessed by all of them must have 
been inherited from a common ancestor, a diagram was made repre- 
senting the hypothetical tracheation of a nymph of the primitive 
winged insect (Fig. 77). In this diagram the tracheag are lettered 




Fig. 77.— Hypothetical tracheation of a wing of the primitive nymph. 

with the abbreviations used in designating the veins that are formed 
about them in the course of the development of the wing. The dia- 
gram will serve, therefore, to indicate the typical venation of an insect 



64 AN INTRODUCTION TO ENTOMOLOGY 

wing, except that the tracheae are not crowded together at the base of 
the wing as are the veins in the wings of adults.* 

Longitudinal veins and cross-veins. — The veins of the wing can be 
grouped under two heads: first, longitudinal veins, those that 
normally extend lengthwise the wing; and second, cross-veins, those 
that normally extend in a transverse direction. 

The insertion of the word normally in the above definitions is 
important; for it is only in comparatively generalized wings that the 
direction of a vein can be depended upon for determining to which of 
these two classes it belongs. 

The principal wing-veins.— The longitudinal wing-veins constitute 
the principal framework of the wings. In the diagram representing 
the typical venation of an insect wing (Fig. 77), only longitudinal 
veins are indicated; this is due to the fact that the diagram was based 
on a study of the tracheation of wings, and in the more generalized 
wings the cross-veins are not preceded by tracheae; moreover in the 
wings of more generalized paleozoic insects there were no definite 
cross-veins, but merely an irregular network of thickened lines 
[)etween the longitudinal veins. 

There are eight principal veins; and of these the second, third, 
fourth, and fifth are branched. The names of these veins and the 
t bbreviations by which they are known are as follows, beginning with 
' he on3 nearest the costal margin of the wing: 

Nam?s of vsins Abbreditions 

Costa C 

Subcosta So 

Radius R 

Media M 

Cubitus Cu 

First Anal ist A 

Second Anal 2dA 

Third Anal 3dA 

The chief branches of the voing-veins. — The chief branches of the 
principal veins are numbered, beginning with the branch nearest to 
the costal margin of the wing. The term used to designate a branch 
of a vein is formed by compounding the name of the vein with a 

*For many details regarding the development of the wings of insects, their 
structure, and the terminology of the wing-veins, that can not be included in 
this work, see a volume by the writer entitled The Wings of Insects. This is 
published by The Comstock Publishing Company, Ithaca, N. Y. 



THE EXTERNAL ANATOMY OF INSECTS 63 

numeral indicating the number cf the branch ; thus, for example, the 
first branch of the radius is radius-one or vein Ri. 

In the case of radius and media, each of which has more than two 
branches, each division of the vein that bears two or more branches 
has received a special name. Thus after the separation of radius-one 
from the main stem of radius there remains a division which is typi- 
cally four-branched; this division is termed the radial sector, or 
vein Rsi the first division of the radial sector, which later separates 
into radius-two and radius-three, is designated as radius-two-plus- 
three or vein R2+3; and the second division is termed radius-four- 
plus-five or vein R4+5. Media is typically separated into two divi- 
sions, each of which is two-branched; the first division is media-one- 
plUs two or vein Mi +2, the second is media-three-plus-four or vein 
M3+4. 

The veins of the anal area.— The three anal veins exhibit a wide 
range of variation both as to their persistence and to their form when 




Fig. 78. — A wing of Rhyphns. 

present. In those cases where the anal veins are branched there is 
no indication that the branching has been derived from a uniform 
primitive type of branching. For this reason in describing a branched 
anal vein merely the nimiber of branches is indicated. 

In some cases, as in the Odonata, there is a single anal vein the 
identity of which can not be determined. In such cases this vein is 
designated merely as the anal vein or vein A, and its branches as Ax, 
Ai, Az, etc. 

The reduction of the number of wing-veins. — In many wings the 
nimiber of the veins is less than it is in the hypothetical type. In 
some cases this is due to the fact that one or more veins have faded 
out in the course of the evolution of the insects showing this deficiency; 
frequently in such wings vestiges of the lacking veins remain, either 
as faint line-s in the positions formerly occupied by the veins or as 



66 AN INTRODUCTION TO ENTOMOLOGY 

short fragments of the veins. A much more common way in which 
the number of veins has been reduced is by the coalescence of adja- 
cent veins. In many wings the basal parts of two or more principal 
veins are united so as to appear as a single vein; and the number of 
the branches of a vein has been reduced in very many cases by two or 
more branches becoming united throughout their entire length. 

When a vein consists of two or more of the primitive veins united, 
the name applied to the compound vein should indicate this fact. In 
the wing of Rhyphus (Fig. 78), for example, radius is only three- 
branched; but it would be misleading to designate these branches as 
Ri, R2, and R3, for this would indicate that veins R4 and R5 are lacking. 
The first branch is evidently Ri ; the second branch is composed of the 




Fig. 79. — A wing of Tabanus. 

coalesced R2 and R3, it is, therefore, designated as R2+3; and the 
third branch, which consists of the coalesced R4 and R5, is designated 
as R4+5. 

A second method of coalescence of veins is illustrated by a wing of 
Tabanus (Fig. 79). In this wing the tips of cubitus-two and the 
second anal vein are united ; here the coalescence began at the margin 
of the wing and is progressing towards the base. The united portions 
of the two veins are designated as 2d A+Cu2. 

When it is desired to indicate the composition of a compound 
vein it can be readily done by combining the terms indicating its 
elements. But in descriptions of hymenopterous wings where a 
compound vein may be formed by the coalescence of several veins the 
logical carrying out of this plan would result in a very cumbersome 
terminology, one that it is impracticable to use in ordinary descrip- 
tions. In such cases the compound vein is designated by the term 
indicating its most obvious element. Thus, for example, in the fore 



THE EXTERNAL ANATOMY OF INSECTS 



67 



wing of Pamphilius, where veins M4, Cu,, and Cu^ coalesce with the 
first anal vein, the united tips of these veins is designated as vein ist A, 
the first anal vein being its most obvious element (Fig. 80), although 
it is really vein M4+Cui+Cu2 + ist A. 

Serial veins. — In the wings of some insects, where the wing-vena- 
tion has been greatly modified, as in certain Hymenoptera, there exist 
what appears to be simple veins that in reality are compound veins 
composed of sections of two or more veins joined end to end with no 
indication of the point of union. Compound veins formed in this 




Fig. 80. — Wings of Pamphilius. 



manner are termed serial veins. Examples of wings in which there are 
serial veins are figured in the chapter treating of the Hymenoptera. 

In designating serial veins either the sign & or a dash is used 
between the terms indicating the elements of the vein, instead of the 
sign -f as the latter is used in designating compound veins formed by 
the coalescence of veins side by side. If the serial vein consists of 
only two elements the sign & is used; thus the serial vein in the wings 
of braconids, which consists of the medial cross-vein and vein M„ is 
designated as m & M2. 

In those cases where sections of several veins enter into the com- 
position of a serial vein, the serial vein is designated by the abbrevia- 
tion of the name of the basal element connected by a dash with the 



68 AN INTRODUCTION TO ENTOMOLOGY 

abbreviation of the name of the terminal element. Thus a serial 
vein, the basal element of which is the cubitus and the terminal ele- 
ment vein Ml, is designated as vein Cit — Mi. A serial vein thus 
formed exists in the hind wings of certain ichneumon flies. 

The increase of the number of wing-veins. In the wings of many- 
insects the number of veins is greater than it is in the hypothetical 
type. This multiplication of veins is due either to an increase in the 




Fig. 8 1 . — Wings of Osmylus hyalinatus. 

nimiber of the branches of the principal veins by the addition of 
secondary branches, termed accessory veins, or to the development of 
secondary longitudinal veins between these branches, termed inter- 
calary veins. In no case is there an increase in the number of principal 
veins. 

The accessory veins. — The wings of Osmylus (Fig. 8i) are an exam- 
ple of wings in which accessory veins have been developed; here the 
radial sector bears many more branches than the typical number; 
those branches that are regarded as the primitive branches are 
lettered Ri, Ro, R3, R4, and R5 respectively (Fig. 82); the other 



THE EXTERNAL ANATOMY OF INSECTS 



69 



branches are the secondarily developed accessor}^ veins. Two types 
of accessory veins are recognized the marginal accessory veins and 
the definitive accessory veins. 

The marginal accessory veins are twig-like branches that are the 
result of bifurcations of veins that have not extended far back from 
the margin of the wing; many such short branches of veins exist in 
the wings of Osmylus (Fig. 8i). The nimiber and position of the 
marginal accessory veins are not constant, differing in the wings of 
the two sides of the same individual. 

The definitive accessory veins differ from the marginal accessory 




Fig. 82. — Base of fore wing shown in Figure 81. 



veins in having attained a position that is comparable in stability to 
that of the primitive branches of the principal veins. 

In those cases where the accessory veins are believed to have been 
developed in regular order they are designated by the addition of a 
letter to the abbreviation of the name of the vein that bears them; 
thus if vein R2 bears three accessory veins they are designated as 
veins R2a, Rsb, and Rac, respectively. 

The intercalary veins. — The intercalary veins are secondarily 
developed longitudinal veins that did not arise as branches of the 
primitive veins, but were developed in each case as a thickened fold in 
a corrugated wing, more or less nearly midway between two pre- 
existing veins, with which primarily it was connected only by cross- 
veins. Excellent examples of unmodified intercalary veins are com- 



70 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. 83. — Wing of a May-fly (After Morgan). 



mon in the Ephemerida, where most of the intercalary veins remain 
distinct from the veins between which they were developed, being 

connected with 
them only by 
cross-veins, the 
proximal end of 
the intercalary 
vein being free 
(Fig. 83). ^ 

When it is 
desirable to re- 
fer to a parti- 
cular interca- 
lary vein it can 
be done by combining the initial /, indicating intercalary, with the 
designation of the area of the wing in which the intercalary vein occurs. 
For example, in the wings of most May-flies there is an intercalary 
vein between veins Cui and Cu2, i e. in the area Cui ; this intercalary 
vein is desig- 
nated as ICui. 
The adven- 
titious veins. — 
In certain in- 
sects there are 
secon d ary 
veins that are 
neither acces- 
sory veins nor 
intercalary 
veins as de- 
fined above; 
these are 
termed adven- 
titious veins. 
Examples of 
these are the 
supplements of 
the wings of 




St A 



3dA 2d A '^ 

Fig. 84. — Wings of Prionoxystus. 

certain Odonata and the spurious vein of the Syrphidae. 

The anastomosis of veins. — The typical arrangement of wing-veins 
is often modified by an anastomosis of adjacent veins; that is, two 



THE EXTERNAL ANATOMY OF INSECTS 



71 



veins will come together at some point more or less remote from their 
extremities and merge into one for a greater or less distance, while 
their extremities remain separate. In the fore wing of Prionoxystus 
(Fig. 84), for example, there is an anastomosis of veins R3 and R4+5. 
The named cross-veins. — In the wings of certain insects, as the 
dragon-flies, May-fiies, and others, there are many cross-veins; it is 
impracticable in cases of this kind to name them. But in several of 
the orders of insects there are only a few cross-veins, and these have 
been named. Figure 85 represents the hypothetical primitive type 



•5^> Sc^ 




Fig. 85. — The hypothetical primitive type of wing-venation with the named 
cross-veins added. 

of wing-venation with the named cross-veins added in the positions in 
which they normally occm-; these are the following: 

The humeral cross-vein (h) extends from the subcosta to costa near 
the humeral angle of the wing. 

The radial cross-vein (r) extends between the two principal divi- 
sions of radius, i. e. from vein Ri to vein Rg. 

The sectorial cross-vein {s) extends between the principal divisions 
of the radial sector — ■ i. e., from vein R2+3 to vein R4+5 or from vein 
R3 to vein R4. 

The radio-medial cross-vein (r — m) extends from radius to media, 
usually near the center of the wing. When in its typical position 
this cross- vein extends from vein R4+5 to vein Mi +2. 

The medial cross-vein (m) extends from vein M2 to vein M3. This 
cross-vein divides cell M2 into cells, ist M2 and 2d M2; see Figure 87 
where the cells are lettered. 

The medio-cubital cross-vein (m — cu) extends from media to 
cubitus. 



72 



AN INTRODUCTION TO ENTOMOLOGY 



The arculus. — In many insects there is what appears to be a cross- 
vein extending from the radius to the cubitus near the base of the 
wing; this is the arculus. The arculus is designated in figures of 
wings by the abbreviation ar. Usually when the arculus is present 
the media appears to arise from it; the fact is, the arculus is com- 
pound, being composed of a section of media and a cross-vein. 

Figure 86 is a dia- 



e+yl/ 




Fig. 86. — Diagram of a:i arculus of a dragon-fly. 



gram representing 
the typical struc- 
ture of the arculus. 
That part of the 
arculus which is a 
section of media is 
designated as the 
anterior arculus (aa) 
and that part formed by a cross-vein, the posterior arculus (pa) . 

The terminology of the cells of the wing. — Each cell of the wing is 
designated by the name of the vein that normally forms its front 
margin when the wings are spread. See Figure 87 where both the 
veins and the cells of the wing are lettered. 

The cells of the wing fall naturally into two groups: first, those 
on the basal part of the wing; and second, those nearer the distal end 
of the wing. The former are bounded by the stems of the principal 
veins, the latter, by the branches of these veins; a corresponding 
distinction is made in designating the cells. Thus a cell lying behind 
the main stem of radius and in the basal part of the wing is designated 
as cell R; while a cell lying behind radius-one is designated as cell Ri. 




zdA 
Fig. 87. — A wing of Rhyphus. 

It should be remembered that the coalescence of two veins results 
in the obliteration of the cell that was between them. Thus when 



THE EXTERNAL ANATOMY OF INSECTS 73 

veins Ri and Rz coalesce, as in the wings of RJtyphus (Fig. 87), the cell 
lying behind vein i?2+3 is cell Rz, and not cell i?2+3, cell i?2 having been 
obliterated. 

When one of the principal cells is divided into two or more parts by 
one or more cross-veins, the parts may be mmibered, beginning v\^ith 
the proximal one. Thus in Rhyphus (Fig. 87), cell M2 is divided by 
the medial cross-vein into cell istM-i and cell 2dM2. 

When two or more cells are united by the atrophy of the vein or 
veins separating them, the compound cell thus formed is designated 
by a combination of the terms applied to the elements of the com- 
pound cell. When, for example, the stem of media is atrophied, the 
cell resulting from the combination of cells R and M is designated as 
cell R+M. 

The application of this system of naming the cells of the wing is an 
easy matter in those orders where there are but few cross- veins; but 
in those orders where there are many cross-veins it is not practicable 
10 apply it. In the latter case we have to do with areas of the wing 
rather than with separate cells. These areas are designated as are the 
cells of the few- veined wings with which they correspond; thus the 
area immediately behind vein R2 is area R2. 

The corrugations of the wings. — The wings of comparatively few 
insects present a flat surface ; in most cases the membrane is thrown 
into a series of folds or corrugations. This corrugating of the wing in 
some cases adds greatly to its strength, as in the wings of dragon-fiies; 
in other cases the corrugations are the result of a folding of the wing 
when not in use, as in the anal area when this part is broadly ex- 
panded. 

It rarely happens that there is occasion to refer to individual 
members of either of these classes of folds, except perhaps the one 
between the costa and the radius, which is the subcostal fold and that 
which is normally between the cubitus and the first anal vein, the 
cubito-anal fold. 

Convex and concave veins. — ^When the wings are corrugated, the 
wing-veins that follow the crests of ridges are termed convex veins; 
and those that follow the furrows, concave veins. 

The furrows of the wing. — There are found in the wings of many 
insects one or more suture-like grooves in the membrane of the wing; 
these are termed the furrows of the wing. The more important of 
these furrows are the four following: 

The anal furrow when present is usually developed in the cubito 
anal fold ; but in the Heteroptera it is found in front of the cubitus. 



74 AN INTRODUCTION TO ENTOMOLOGY 

The median furrow is usually between radius and media. 

The nodal furrow is a transverse suture beginning at a point in the 
costal margin of the wing corresponding to the nodus of the Odonata 
and extending towards the inner margin of the wing across a varjdng 
number of veins in the different orders of insects. 

The axillary furrow is a Hne that serves as a hinge which facilitates 

the folding of the posterior lobe of the wing of many insects under that 

^^^^^^ part of the wing 

\ \ ^"\^ J^cr^^^*^*"'^"""'"'^--^^/"'^'''^ wing where they 

VJ ^■-~— J^N ^^r^"""^^ ^""""""^y^ ^'"^ crossed by 

^^^^---—J N ^^^ ^--^"^^ furrows. The 

bullae are usually 
Fig. 88. — Wings of Myrmeaa; b, b, b, hullse. , . , 

paler m color 

than the other portions of the wing; they are common in the wings 

of the Hymenoptera (Fig. 88), and of some other insects. 

The ambient vein. — Sometimes the entire margin of the wing is 
stiffened by a vein-like structure; this is known as the ambient vein. 

The humeral veins. — In certain Lepidoptera and especially in the 
Lasiocampidae, the humeral area of the hind wings is greatly expanded 
and in many cases is strengthened by the development of secondary 
veins. These are termed the humeral veins. 

TJie pterostigma or stigma. — A thickened, opaque spot which 
exists near the costal margin of the outer part of the wing in many 
insects is known as the pterostigma or stigma. 

The epipleurcB. — A part of the outer margin of the elytra of beetles 
when turned down on the side of the thorax is termed the epipleura. 

The discal cell and the discal vein. — The term discal cell is applied 
to a large cell which is situated near the center of the wing ; and the 
term discal vein, to the vein or series of veins that limits the outer end 
of the discal cell. These terms are not a part of the uniform terminol- 
ogy used in this book, and can not be made so, being applied to 
different parts of the wing by writers on different orders of insects. 
They are included here as they are frequently used, as a matter of 
convenience, by those who have adopted the uniform terminology. 
The discal cell of the Lepidoptera is cell R+M+ISIM2; that of th-* 
Diptera is cell ist M2; and that of the Trichoptera is cell R2+3. 



THE EXTERNAL ANATOMY OF INSECTS 75 

The anal area and the preanal area of the wing. — In descriptions of 
wings it is frequently necessary to refer to that part of the wing 
supported by the anal veins ; this is designated as the anal area of the 
wing; and that part lying in front of the anal area, including all cf 
the wing except the anal area, is termed the preanal area. 

IV. THE ABDOMEN 

a. THE SEGMENTS OF THE ABDOMEN 

The third and terminal region of the bDdy, the abdomen, consists 
of a series of approximately similar segments, which as a rule are 
without appendages excepting certain segments near the caudal end 
of the body. 

The body-wall of an abdominal segment is usually comparatively 
simple, consisting in adults of a tergum and a sternum, united by 
lateral conjunctivas. Somstimas there are one or two small sclerites 
on each lateral aspect of a segment; these are probably reduced 
pleura. 

The nimiber of segments of which the abdomen appears to be 
composed varies greatly in different insects. In the cuckoo-flies 
(Chrysididag) there are usually only three or four visible; while in 
many insects ten or eleven can be distinguished. All intergrades 
between these extremes occur. 

The apparent variation in the nimiber of abdominal segments is 
due to two causes: in some cases, some of the segments are tele- 
scoped ; and in others, adjacent segments coalesce, so that two or more 
segments appear as one. 

A study of embryos of insects has shown that the abdomen con- 
sists typically of eleven segments; although this number may be 
reduced during the development of the insect by the coalescence of 
adjacent segments. 

In some insects there is what appears to be a segment caudad of 
the eleventh segment; this is termed the telson. The telson differs 
from the segments preceding it in that it never bears appendages. 

Special terms have been applied, especially by writers on the 
Coleoptera, to the caudal segments of the abdomen. Thus the 
terminal segment of a beetle's abdomen when exposed beyond the 
elytra is termed the pygidium; the tergite cephalad of the pygidium, 
especially in beetles with short elytra, the propygidium; and the last 
abdominal stemite, the hypopygium. The term hypopygium is also 
applied to the genitalia of male Diptera by writers on that order of 
insects. 



76 



AN INTRODUCTION TO ENTOMOLOGY 




b. THE APPENDAGES OF THE ABDOMEN 

In the early embryonic stages of insects, each segment of the 
abdomen, except the telson, bears a pair of appendages (Fig. 89) . This 
indicates that the primitive ancestor of insects possessed many legs, 
like a centipede. But the appendages of the first 
seven abdominal segments are usually lost during 
embryonic life, these segments being without appen- 
dages in postembryonic stages, except in certain 
Thysanura and Collembola, and in some larvae. 

Reference is made here merely to the primary 
appendages of the segments, those that are homodyna- 
mous with the thoracic legs; secondarily developed 
appendages, as for example, the tracheal gills, are 
present in the immature instars of many insects. 
The styli or vestigial legs of certain Thysanura. — ^In 
certain Thysanura the coxa of each middle and hind 
thoracic leg bears a small appendage, the stylus (Fig. 90) ; 
and on from one to nine abdominal segments there is 
a pair of similar styli. These abdominal styli are 
believed to be homodynamous with those of the thoracic 
legs, and must, therefore, be regarded as vestiges of 
abdominal legs. 

The collophore of the CoUembola.— Although in the 
postembryonic stages of Collembola the collophore is 
an unpaired organ on the middle line of the ventral aspect of the first 
abdominal segment, the fact that it arises in the embryo as a pair of 
appendages comparable in position to the thoracic legs, has led to the 
beHef that it represents the legs of this segment. The structiire of 
the collophore is described more fully later in the chapter treating of 
the Collembola. 

The spring of the Collembola. — The spring of the Collembola, 
like the collophore, is believed to represent a pair of primary append- 
ages. This organ is discussed in the chapter treating of the Col- 
lembola. 

The genitalia. — In most insects there are more or less prominent 
appendages connected with the reproductive organs. These append- 
ages constitute in males the genital claspers and in females the ovi- 
positor; to them have been applied the general term genitalia, they 
are also known as the gonapophyses. 

The genitalia, when all are developed consist of three pairs or 
appendages. Writers vary greatly in their views regarding the seg- 



Fig. 89.- Em- 
bryo of Hy- 
dro philus 
showing ab- 
dominal ap- 
pendages. 



THE EXTERNAL ANATOMY OF INSECTS 



77 



ments of the abdomen to which these appendages belong. One cause 
of difference is that some writers regard the last segment of the abdo- 
men as the tenth abdominal 
segment while others believe it 
to be the eleventh, which is 
the view adopted in this work, 
this segment bears the cerci 
when they are present. The 
three pairs of appendages that 
constitute the genitalia are 
borne by the eighth and ninth 
segments, two pairs being 
borne by the ninth segment. 
The outer pair of the ninth 
segment constitute the sheath 
of the ovipositor. See ac- 
count of the genitalia of the 
Orthoptera in Chapter eight. 

The genitalia of many in- 
sects have been carefully fig- 
ured and described and special 
terms have been applied to 
each of the parts. But as most 
of these descriptions have been 
based upon studies of repre- 
sentatives of a single order of 
insects or even of some smaller 
group, there is a great lack 
of uniformity in the terms 
applied to homologous parts 
in the different orders of in- 
sects; such of these terms as 
are commonly used are defined 

later in the characterizations of the several orders of insects. 

The cerci. — In many insects there is a pair of caudal appendages 

which are known as the cerci; these are the appendages of the 

eleventh abdominal segment, the last segment of the body except in 

the few cases where a telson is presemt. 

The cerci vary greatly in form ; in some insects, as in most Thy- 

sanura, in the Plecoptera, and in the Ephermerida, they are long and 




Fig. 90. — Ventral aspect of Machilis; c, cer- 
cus; Ip, labial palpus; mf, median caudal 
filament; mp, maxillary palpus; 0, oviposi- 
tor; .s, s, styli. That part of the figure 
representing the abdomen is after Oude- 
mans. 



78 



AN INTRODUCTION TO ENTOMOLOGY 



many jointed; while in others they are short and not segmented. 

The function of the cerci is different in different insects ; they are 
beheved to be tactile in some, olfactory in others, 
and in some males they aid in holding the female 
during copulation. 

The median caudal filament. — In many of the 
Ephemerida and in some of the Thysanura, the last 
abdominal segment bears a long, median filament, 
which resembles the many-jointed cerci of these 
insects (Fig. 91); this filament is believed to be a 
prolongation of the tergum of this segment and not a 
true appendage like the cerci. 

The prolegs of larvae. — ^The question whether the 
prolegs of larv^ee represent true appendages or are 
merely hypodermal outgrowths has been much dis- 
cussed. Several embryologists have shown that in 
embryos of Lepidoptera and of saw-flies limb-rudi- 
ments appear on all or most of the abdominal seg- 
ments; and that they very soon disappear on those 
segments which in the larva have no legs while on other segments 
they are transferred into functional prolegs. If this view is estab- 
lished we must regard such prolegs as representing primitive abdo- 
minal appendages, that is as true abdominal legs. 




Fig. 91. — Lepis- 
ma saccharina. 



V. THE MUSIC AND THE MUSICAL ORGANS 
OF INSECTS 

Much has been written about music ; but the greater part of this 
literature refers to music made by man for human ears. Man, how- 
ever, is only one of many musical animals; and, although he excels 
all others in musical accomplishments, a study of what is done by our 
htmibler relatives is not without interest. 

The songs of birds command the attention of all observers. But 
there is a great orchestra which is performing constantly through the 
warmer portions of the year, which is almost unnoticed by man.. 
Occasionally there is a performer that cannot be ignored, as: — • 

"The shy Cicada, whose noon- voice rings 
So piercing shrill that it almost stings 
The sense of hearing." (Elizabeth Akers.) 

But the great majority fiddle or drum away unnoticed by human ears. 



THE EXTERNAL ANATOMY OF INSECTS 79 

Musical sounds are produced by many different insects, and in 
various ways. These sounds are commonly referred to as the songs of 
insects; but properly speaking few if any insects sing; for, with some 
possible exceptions, the note of an insect is always at one pitch, lacking 
musical modulations like those of the songs of man and of birds. 

The sound produced by an insect may be a prolonged note, or it 
may consist of a series of short notes of varying length, with intervals 
of rest of varying lengths. These variations with differences in pitch 
give the wide range of insect calls that exists. 

In some cicadas where the chambers containing the musical organs 
are covered by opercvda, the insect can give its call a rhythmic 
increase and decrease of loudness, by opening and closing these 
chambers. 

As most insect calls are strident, organs specialized for the pro- 
duction of these calls are commonly known as stridulating organs. 
But many sounds of insects are produced without the aid of organs 
specialized for the production of sound. The various ways in which 
insects produce sounds can be grouped under the following heads : 

First. — By striking blows with some part of the body upon sur- 
roimding objects. 

Second. — By rapid movements of the wings. In this way is 
produced what may be termed the music of flight. 

Third. — By rasping one hard part of the body upon another. 
Under this head fall the greater number of stridulating organs. 

Fourth. — By the rapid vibration of a membrane moved by a muscle 
attached to it. This is the type found in the cicadas. 

Fifth. — By the vibration of msmbranss set in motion by th^ rush 
of air through spiracles. The reality of this method has been ques- 
tioned. 

Sixth. — By rapid changes of the outline of the thorax due to the 
action of the wing muscles. 

a. SOUNDS PRODUCED BY STRIKING OBJECTS OUTSIDE THE BODY 

Although th3 sDunis prolu^sl by in332'3 by stri'.clng blows with 
some part of ths bDiy upon surrounding objects are not rapid enough 
to give a musical note, they are referred to here for the sake of 
completeness. 

The most familiar SDunis of this kind are those produced by the 
insects known as the dsath-watch. These are small beetles of the 
family Ptinidas, and espscially those of the genus Anobium. These 
are wood-boring insects, frequently found in the woodwork of old 



80 AN INTRODUCTION TO ENTOMOLOGY 

houses and in furniture, where they make a ticking sound by striking 
their heads against the walls of their burrows. The sound consists of 
several, sharp, distinct ticks, followed by an interval of silence, and is 
beheved to be a sexual call. 

The name death-watch was applied to these insects by supersti- 
tious people who believed that it presaged the death of some person 
in the house where it is heard. This belief probably arose from the 
fact that the sound is most likely to be heard in the quiet of the night, 
and would consequently be observed by watchers by sick-beds. 

The name death-watch has also been applied to some species of the 
Psocidas, Clothilla pulsatoria and Atropos divinatoria, which have been 
believed to make a ticking sound. This, however, is doubted by 
some writers, who urge that it is difficult to believe that such minute 
and soft insects can produce sounds audible to human ears. 

The death-watches produce their sounds individually; but an 
interesting example of an insect chorus is cited by Sharp ('99, p. 156), 
who, quoting a Mr. Peal, states that an ant, presimiably an Assamese 
species, "makes a concerted noise loud enough to be heard by a human 
being at twenty or thirty feet distance, the sound being produced by 
each ant scraping the horny apex of the abdomen three times in rapid 
succession on the dry, crisp leaves of which the nest is usually com- 
posed." 

h. THE MUSIC OF FLIGHT 

The most obvious method by which insects produce sounds is by 
beating the air with their wings during flight. It can be readily seen 
that if the wing-strokes are sufficiently rapid and are uniform, they 
will produce, like the flapping reeds of a mouth organ, a musical note. 

When, however, we take into account the fact that to produce the 
lowest note regularly employed in music, the C of the lowest octave, 
requires 32 vibrations a second, i. e., nearly 2,000 vibrations per 
minute, it will seem marvellous that muscular action can be rapid 
enough to produce musical notes. Nevertheless, it is a fact that 
many insects sing in this way ; and too their notes are not confined to 
the lower octaves. For example, the common house fly hums F of 
the middle octave, to produce which, it must vibrate its wings 345 
times per second or 20,700 times per minute. 

As a rule, the note produced by the wings is constant in each 
species of insect. Still with insects, as with us, the physical condition 
of the singer has its influence. The vigorous honey-bee makes the A 
of 435 vibrations, while the tired one hums on the E of ^26 vibrations. 



THE EXTERNAL ANATOMY OF INSECTS 81 

While it is only necessary to determine the note produced by 
vibrating wings to ascertain the rate of vibration, a graphical demon- 
stration of the rate is more convincing. Such a demonstration has 
been made by Marey ('69) who fixed a fly so that the tip of the wing 
just touched the smoked surface of a revolving cylinder, and thus 
obtained a wavy line, showing that there were actually 320 strokes in 
a second. This agrees almost exactly with the number inferred from 
the note produced. 

The music of flight may be, in many cases, a mere accidental result 
of the rapid movement, and in no sense the object of that movement, 
like the hwoa of a trolley car; but there are cases where the song seems 
to be the object of the movement. The honeybee produces different 
sounds, which can be understood by man, and probably by bees, as 
indicating different conditions. The contented hum of the worker 
collecting nectar may be a song, like the well-known song of a hen 
wandering about on a pleasant day, or may be an accidental sound. 
But the honeybee produces other sounds that communicate ideas. 
The swarming sound, the hiim of the queenless colony, and the note 
of anger of a belligerent bee can be easily distinguished by the experi- 
enced beekeeper, and doubtless also by the bee colony. It seems 
probable, therefore, that in each of these cases the rate of vibration of 
the wings is adjusted so as to produce a desired note. This is also 
probably true of the song of the female mosquito, which is pitched so 
as to set the antennal hairs of the male in vibration. 

While the music of flight is a common phenomenon, many insects 
have a silent flight on account of the slowness of the wing-movement. 



C. STRIDULATING ORGANS OF THE RASPING TYPE 

The greater number of the insect sounds that attract our attention 
are produced by the friction of hard parts of the cuticula by which a 
vibrating surface is set in motion. In some cases, as in many of the 
Orthoptera, the vibrating surface is apart of the wings that is special- 
ized for this purpose; but in other cases, a specialized vibrating sur- 
face has not been observed. 

Stridulating organs of the rasping type are possessed by represen- 
tatives of several of the orders of insects ; but they are most common 
in the order Orthoptera, and especially in the families Acridiidae, 
Locustidffi, and Gryllidae, where the males of very many species 
possess them. Very few other Orthoptera stridulate; and with few 
exceptions it is only the males that sing. 



82 



AN INTRODUCTION TO ENTOMOLOGY 



In each of these famiHes the vibrating element of the stridulating 
organ is a portion of one or of both of the fore wings ; but this is set in 
motion in several different ways. In some exotic Acridiidas abdominal 
stridulating organs exist. 

The stridulating organs of the Locustidae. — With many species 
of the Locustidffi we find the males furnished with stridulating organs ; 
but these are comparatively simple, and are used only in the day time. 
Two methods of stridulation are used by members of this family. 
The simpler of these two methods is employed by several common 
species belonging to the (Edipodinae; one of which is the Carolina 
locust, Dissosteira Carolina, whose crackling flight is a common feature 
of country roadsides. These locusts, as they fly, rub the upper sur- 
face of the costal margin of the hind wings upon the lower surface of 
the thickened veins of the fore wings, and thus produce a loud but not 
musical sound. 

The second method of stridulation practiced by locusts consists 
in rubbing the inner surface of the hind femora, upon each of which 
there is a series of bead-like prominences (Fig. 92), against the outer 

surface of the fore wings. 
With these insects, there is a 
thickening of the radius in the 
basal third of each fore wing, 
and a widening of the two 
areas between this vein and 
the costal margin of the wing, 
which serves as a sounding 
board (Fig. 93). The two 
wings and femora constitute a 
pair of violin-like organs; the thickened radius in each case cor- 
responding to the strings; the membrane of the wing, to the body 
of the instrument ; and the file of the femur, to the bow. These two 
organs are used simultaneously. When about to stridulate, the insect 




B-- 



Fig. 92. — A, hind femora of Stenobothrus ; 
B, file greatly enlarged. 




Fig- 93- — Fore wing of a male of Stenobothrus. R, radius; Sc, subcosta; 
C, costa. 



THE EXTERNAL ANATOMY OF INSECTS 



83 




places itself in a nearly horizontal position, and raising both hind legs 
at once rasps the femora against the outer surface of the wings. The 
most common representatives of insects that 
stridulate in this way belong to the genus Steno- 
bothrus. 

The stridulating organs of the Gryllidae and 
the Tettigoniidae. — The stridulating organs of 
the Gryllidae and the Tettigoniidae are of the same 
type, and are the most highly specialized found in 
the Orthoptera. They consist of modified portions 
of the fore wings ; both the vibrating and the rasp- 
ing elements of the organs pertaining to the wings. 
It is by rubbing the two fore wings together 
that sound is produced. 

In what is probably the more generalized con- 
dition of the organs, as seen in Gryllns, each 
fore wing bears a rasping organ, the file (Fig. 
; 94, /) a hardened area, the scraper (Fig. 94, s), 
\:,^^^^^^ 1,^-4^ against which the file of the other wing acts, and 
'Itli 'Eli 1:1:^0 vibrating areas, the tympana (Fig. 94, /, t). As 
rm^^?^' ^?^^ '^^ ^ the file of either wing can be used to set the 
C tympana of the wings in vibration, we may say 

Fig.94.— Fore wing of that Grylliis is ambidextrous. 

Grvllus; A, as seen 1 , • 1,1 

from above, that When the cncket wishes to make his call, he 

part of the wmg elevates his fore wings so that thev make an angle 
which IS bent down ^° .'i,, , 

on the side of the of about forty-five degrees with the body; then 

abdomen is not holding them in such a position that the scraper 

shown; 5, scraper;/, , „, ^ , - , 

t, tympana. B,base of one rests on the file of the other, he moves the 

of wing seen from ^^jngg ^^ck and forth laterally, so that the file and 
below; s, scraper; , , ^, . , 

/.file. C, file great- scraper rasp upon each other. Ihis throws the 
ly enlarged. wings into vibration and produces the call. 

It is easy to observe the chirping of crickets. If one will move 
slowly towards a cricket that is making his call, and stop when the 
cricket stops chirping until he gains confidence and begins again, 
one can get sufficiently near to see the operation clearly. This can 
be done either in the day time or at night with the aid of a light. 

The songs of the different genera of crickets can be easily dis- 
tinguished, and that of each species, with more care. Writers on the 
Orthoptera have carefully described the songs of our more common 
crickets, and especially those of the tree crickets. The rate of chirping 



84 



AN INTRODUCTION TO ENTOMOLOGY 



is often influenced by temperature, being slower in cool nights than 
in warm ones; and becoming slower towards morning if the tem- 
perature falls. 

In certain genera of crickets as Nemohins and QLcanthus, while 
each fore wing is furnished with a file and tympana, the scraper of the 
right wing is poorly formed and evidently not functional. As these 
insects use only the file of the right wing to set the tympana of the 
wings in vibration, they may be said to be right-handed. 




Fig- 95- — Wings of a female nymph of CEcanthus (From Comstock and 
Needham). 

In the Locustidag a similar modification of the function of the 
stridulating organs has taken place. In all of our common represen- 
tatives of the family, at least, only one of the files is used. But in 
these cases it is the file of the left wing that is functional ; we may say, 
therefore, that so far as observed the Locustidas are left-handed. 
Different genera exhibit great differences as to the extent of the reduc- 
tion of the unused parts of the stridulating organs. The file is 
present in both wings of all of the forms that I have studied; but th2 
unused file is sometimes in a vestigial condition. The scraper is less 
persistent, being frequently entirely lacking in one of the wings. In 
some cases, the tjmipana of one wing have been lost; but in others 
the tympana of both wings are well preserved, although only one file 



THE EXTERNAL ANATOMY OF INSECTS 85 

is used. In these cases it is probable that the tympana of both wings 
are set in vibration by the action of the single functional file. 

The determination of the homologies of the parts of the wing that 
enter into the composition of the stridulating organs was accomplished 
by a study of the tracheation of the wings of nymphs (Comstock and 
Needliam, 'gS-'gg). The results obtained by a study of the wings of 
CEcanthus will serve as an illustration. 

Figure 95 represents the wings of a female n3miph of this genus, 
with the tracheag lettered. The only parts to which we need to give 
attention in this discussion are the cubital and anal areas of the fore 
wing; for it is this part of the wing that is modified in the male to 
form the musical organ. Both branches of cubitus are present, and 
Cui bears three accessory branches. The three anal tracheae are 
present and are quite simple. 




Fig. 96. — Fore wing of a male nymph of CEcanthus (From Comstock and 
Needham). 

The homologies of the tracheae of the fore wing of a male nymph, 
Figure 96, were easily determined by a comparison with the trachese 
of the female. The most striking difference between the two sexes 
is a great expanding of the area between the two branches of cubitus 
in the male, brought about by the bending back of the basal part 

of CU2. 

The next step in this study was to compare the wing of an adult 
male, Figure 97, with that of the n5nnph of the same sex; and the 
solution of the problem was soon reached. It can be easily seen that 
the file is on that part of Cu2 that is bent back toward the inner mar- 
gin of the wing (Fig. 97, /); the tympana are formed between the 
branches of cubitus (Fig. 97, /, t); and the scraper is formed at the 
outer end of the anal area (Fig. 97,5). 



86 



AN INTRODUCTION TO ENTOMOLOGY 



A similar study was made of the wings of Conocephalus, as an 
example of the Tettigoniidse, Figure 98 represents the wings of a 

male nymph; 
and Figure 99 
the fore wing 
of an adult. 
The most 
striking fea- 
ture and one 
characteris- 
tic of the fam- 
ily, is that the 
musical organ 
occupies an 
area near the 
base of the 
wing which is 
small corn- 




Fig. 97. — Fore wing of an adult male of CEcanthus;f, vein 
bearing the file; s, scraper; t, t, tympana. 



pared with the area occupied by the musical organs of the Gryllidffi. 
But here, as in the Gryllidse, the file is borne by the basal part of CU2, 




Pig. 98. — Wings of a male nymph of Conocephalus, (From Comstock and 
Needham). 

the tympana are formed between the branches of cubitus, and the 
scraper is formed at the outer end of the anal area. 



THE EXTERNAL ANATOMY OF INSECTS 



87 



Rasping organs of other than orthopterous insects. — Rasping 
organs are found in many other than orthopterous insects and vary 

M 




Fig. 99. — Right fore wing of an adult male of Conocephalus, seen 
from below; /, file; s, scraper. 

greatly in form and in their location on the body. Lack of space for- 
bids any attempt to enimierate these variations here ; but examples of 
various types of stridulating organs will be described in later chapters 
when treating of the insects that possess them. As in the Orthoptera, 
they consist of a rasp and a scraper. The rasp is a file-like area of the 
surface of a segment of the body or of an appendage; and the scraper 
is a hard ridge or point so situated that it can be drawn across the rasp 

by movements 
of the body or 
of an append- 
age. In some 
cases the ap- 
paratus con- 
sists of two 
rasps so situ- 
ated that they 
can be rubbed 
together. 

With many 
beetles one of 




a- 

Fig. 100. — Stridulating organ of an ant, 
(From Sharp after Janet); d, scraper; 



Myrmica rubra 
e, file. 



the two parts of the stridulating organ is situated upon the elytra; 
and it is quite probable that in these cases the elytra acts as vibrating 
surfaces, as do the wings of locusts and crickets. But in many 
cases as where a part of a leg is rubbed against a portion of a 
thoracic segment, there appears to be no vibrating surface unless it is 
the wall of the body or of the appendage that acts as a sounding 
board. In the stridulating organ of Myrmica rubra, var. IcBvinodis, 
figured by Janet (Fig. 100), the scraper is the posterior border of 
one abdominal segment, and the file is situated on the dorsimi of 
the following segment. It is quite conceivable that in this case 



88 AN INTROD UCTION TO ENTOMOLOG Y 

the dorsal wall of the segment bearing the file is made to vibrate 
by the successive impacts of the scraper upon the ridges of the 
file. In fact this seems to me more probable than that the 
sound produced is merely that of the scraper striking against the 
successive ridges of the file. There is at least one recorded case 
where the body wall is specialized to act as a sounding board. 
According to Sharp ('95, p. 200), in the males of the Pneumorides, 
a tribe of South African AcridiidcC, where the phonetic organ is 
situated on the abdomen, this part is inflated and tense, no 
doubt with the result of increasing the volume and quality of the 
sound. 

Ordinarily the stridulating organs of insects are fitted to produce 
notes of a single degree of pitch; but Gahan ('00) figures those of 
some beetles that are evidently fitted to produce sounds of more than 
one degree of pitch ; the file of Hispopria foveicollis, consists of three 
parts, one very finely striated, followed by one in which the striae are 
much coarser, and this in turn followed by one in which the striation 
is intermediate in character between the other two. 

While the stridulating organs of the Orthoptera are possessed 
almost exclusively by the males, in the Coleoptera, very many species 
of which stridulate, the phonetic organs are very commonly possessed 
by both sexes, and serve as a mutual call. In one genus of beetles, 
Phonapate, stridulating organs have been found only in the females 
(Gahan, '00). 

It seems evident that in the great majority of cases the sounds 
produced by insects are sexual calls; but this is not always so. It 
was pointed out long ago by Charles Darwin that "beetles stridulate 
under various emotions, in the same manner as birds use their voices 
for many purposes besides singing to their mates. The great Chiasog- 
nathus stridulates in anger or defiance ; many species do the same from 
distress or fear, if held so that they cannot escape; by striking the 
hollow stems of trees in the Canary Islands, Messrs. Wollaston and 
Crotch were able to discover the presence of beetles belonging to the 
genus Acalles by their stridulation. Lastly the male Ateuchus 
stridulates to encourage the female in her work and from distress 
when she is removed" {The Descent of Man). 

The most remarkable case where stridulating organs have been 
developed for other than sexual purposes is that of the larvae of certain 
Lucanidas and Scarabaeidas described by Schiodte ('74). In these 
larvae there is a file on the coxa of each middle leg, and the hind legs 
are shortened and modified so as to act as scrapers. The most highly 



THE EXTERNAL ANATOMY OF INSECTS 



89 



Specialized example of this type of stridulating organ is possessed by 
the larvae of Passalus, in which the legs of the third pair are so much 

shortened that the 
f.-^...4 , larvae appear to 

have only four legs ; 
each hind leg is a 
paw-like structure 
fitted for rasping 
the file (Fig. loi). 

These insects 
are social, a pair of 
beetles and their 
progeny living to- 
gether in decaying 
wood. The adults 
prepare food for the 
larv«; and the col- 
ony is able to keep 
together by stridu- 
latory signals. 

d. THE MUSICAL 
ORGANS OF A CICADA 

With the cica- 
das there exists a 
type of stridulating 
organ peculiar to 
them, and one that is the most complicated organ of sound 
found in the animal kingdom. Yet, while the cicadas are the 
most noisy of the insect world, the results obtained by their com- 
plicated musical apparatus are not comparable with those pro- 
duced by the comparatively simple vocal organs of birds and of 




Fig. loi. — Stridulating organ of a larva of Passalus; 
a, b, oortions of the metathorax; c. coxa of the 
second leg; d. file; e. basal part of femur of middle 
le?; /, hairs with chitinous process at base of each; 
g, the diminutive third leg modified for scratching 
the file (From Sharp). 



It is said that in some species of Cicada both sexes stridulate; but 
as a rule the females are mute, possessing only vestiges of the musical 
apparatus. 

The structure of the stridulating organs varies somewhat in 
details in different species of Cicada; but those of Cicada pleheia, 
which were described and figured by Carlet ('77), may be taken as an 
example of the more perfect f orn: . In the male of this species there is 
a pair of large plates, on the ventral side of the body, that extend back 



90 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. 1 02. — The musical apparatus of a cicada; fm, 
folded membrane; /, base of leg; Ic, lateral cavity; 
m, mirror; o, operculum, that of the opposite 
side removed; sp, spiracle; t, timbal; vc, ventral 
cavity (After Carlet). 



from the hind border of the thorax and overlap the basal part of the 
abdomen; these are the opercula (Fig. 102, o). The opercula are 
expansions of the ster- 
nellum of the meta- / 

thorax, and each • 

serves as a lid covering 
a pair of cavities, con- 
taining the external 
parts of the musical 
apparatus of one side 
of the body. 

The two cavities 
covered by a single 
operculum may be de- 
signated as the ventral 
cavity (Fig. 102, v. c.) 
and the lateral cavity 
(Fig. 102, /. c.) respec- 
tively. Each cavity is form.ed by an infolding of the body-wall. 

In the walls of these cavities are three membranous areas; these 
are known as the timbal, the folded membrane, and the mirror. 

The timbal is in the lateral cavity on the lateral wall of the parti- 
tion separating the two cavities (Fig. 102, t); the other two mem- 
branes are in the ventral cavity. The folded membrane is in the 
anterior wall of the ventral cavity (Fig. 102, /. m.); and the mirror 
is in the posterior wall of the same cavity (Fig. 102, w). Within the 
body, there is in the region of the musical apparatus a large thoraco- 
abdominal air chamber, which communicates with the exterior 
through a pair of spiracles (Fig. 102 sp); and a large muscle, which 
extends from the furca of the second abdominal segment to the inner 
face of the timbal. 

By the contraction of this muscle the timbal is pulled towards the 
center of the body ; and when the muscle is relaxed, the elasticity of 
the chitinous ring supporting the timbal causes it to regain its former 
position. By a very rapid repetition of these movements of the timbal 
the sound is produced. 

It is probable that the vibrations of the timbal are transmitted to 
the folded membrane and to the mirror by the air contained in the 
large air chamber mentioned above; as the strings of a piano are 
made to vibrate by the notes of a near-by violin. The sound, how- 
ever, is produced primarily by the timbal, the destruction of which 



THE EXTERNAL ANATOMY OF INSECTS 91 

renders the insect a mute; while the destruction of the other mem- 
branes, the timbal remaining intact, simply reduces the sound. 

The chief function of the opercula is doubtless the protecting of 
the delicate parts of the musical organ; but as they can be lifted 
slightly and as the abdomen can be moved away from them to some 
extent, the chambers containing the vibrating parts of the organ can 
be opened and closed, thus giving a rhythmic increase and decrease of 
the loudness of the call. 

e. THE SPIRACULAR MUSICAL ORGANS 

There has been much discussion of the question whether insects, 
and especially Diptera and Hymenoptera, possess a sound -producing 
organ connected with the spiracles or not. Landois ('67) believed 
that he found such an organ and figures and describes it in several 
insects. It varies greatly in form in different insects. In the Diptera 
it consists of a series of leaf-like folds of the intima of the trachea; 
these are held against each other by a special himiming ring, which 
lies close under the opening of the spiracle; and is found within two 
or all four of the thoracic spiracles. These membranous folds of the 
intima are set in vibration by the rush of air through the spiracles. 

In the May-beetle, according to Landois, a buzzing organ is found 
near each of the fourteen abdominal spiracles. It is a tongue-like 
fold projecting into the lumen of the trachea under the base of the 
closing apparatus. On its upper surface it is marked with very fine 
arched furrows. He concludes that this tongue is put in vibration by 
tlie breathing of the insect, and hence the buzzing of the flying beetle. 

If insects produce sounds in the way described by Landois they 
have a voice quite analogous to our own. But the validity of the 
conclusions of Landois has been seriously questioned; the subject, 
therefore, demands further investigation. See also Duncan ('24). 

/. THE ACUTE BUZZING OF FLIES AND BEES 

Many observers have found that when the wings of a fly or of a bee 
are removed or held so that they can not vibrate the insect can still 
produce a sound. The sound produced under these circumstances is 
higher, usually an octave higher, than that produced by the w:n;^^s. 
It is evident, therefore, that these insects can produce sounds in two 
ways; and an extended search has been made for the organ or organj 
producing the higher note. 



92 AN INTRODUCTION TO ENTOMOLOGY 

Landois believed that the spiracular organs referred to above were 
the source of the acute sound. But more recently Perez ('78) and 
Bellesme ('78) have shown that when the spiracles are closed artifi- 
cially the insect can still produce the high tone. Perez attributes the 
sound to the vibrations of the stumps of the wings against the solid 
parts which surround them or of the sclerites of the base of the wing 
against each other. But Bellesme maintains that the sound is pro- 
duced by changes in the form of the thorax due to the action of the 
wing-muscles.* When the wing-muscles are at rest the section of this 
region, according to this writer, represent an ellipse elongated ver- 
tically; the contraction of the muscles transforms it to an ellipse 
elongated laterally; the thorax, therefore, constitutes a vibrating 
body which moves the air like a tine of a tuning fork. Bellesme 
states that by fastening a style to the dorsal wall of the thorax he 
obtained a record of the rate of its vibrations, the ntmiber of which 
corresponded exactly to that required to produce the acute sound 
which the ear perceives. 

The fact that the note produced when the wings are removed is 
higher than that produced by the wings is supposed by Bellesme to be 
due to the absence of the resistance of air against the wings, which 
admits of the maximum rate of contraction of the wing-muscles. 



g. MUSICAL NOTATION OF THE SONGS OF INSECTS 

Mr. S. H. Scudder ('93) devised a musical notation by which the 
songs of stridulating insects can be recorded. As the notes are always 
at one pitch the staff in this notation consists of a single horizontal 
line, the pitch being indicated by a separate statement. Each bar 
represents a second of time, and is occupied by the equivalent of a 

semibreve ; consequently a quarter note 1, or a quarter rest *1, repre- 

^ 

sents a quarter of a second ; a sixteenth note t, or a sixteenth rest \ 

a sixteenth of a second and so on. For convenience's sake he intro- 
duced a new form of rest, shown in the second example given below, 
which indicates silence through the remainder of a measure; this 
differs from the whole rest commonly employed in musical notation 
by being cut off obliquely at one end. 



*This view was maintained by Siebold at a much earlier date in his Anatomy 
of the Invertebrates. 



THE EXTERNAL ANATOMY OF INSECTS 93 

The following examples taken from his paper on "The Songs of 
our Grasshoppers and Crickets" will serve to illustrate this method 
of notation. 

The chirp of Gryllotalpa horealis (Fig. 103) "is a guttural sort of 
sound, like grii or greeu, repeated in a trill indefinitely, but seldom 

grQ gru gru gru grS grfl grQ prn gru grtt^ 

Fig. 103. — The chirp of Gryllotalpa horealis (From Scudder). 

lor more than two or three minutes, and often for less time. It is 
pitched at two octaves above middle C." 

Fig. 104. — The chirp of the katydid (From Scudder). 

The note of the true katydid, Cyrtophylhis concavus, (Fig. 104) 
"which sounds like xr, has a shocking lack of melody; the poets who 
have sung its praises must have heard it at a distance that lends 
enchantment." "They ordinarily call 'Katy' or say 'She did' rather 
than 'Katy did'; that is they rasp their fore wings twice more fre- 
quently than thrice." Mr. Scudder in his account of this song fails 
to indicate its pitch. 

h. INSECT CHORUSES 

Most insect singers are soloists, singing without reference to other 
singers or in rivalry with them. But there are a few species the 
members of which sing in unison with others of their kind that are 
near them. The most familiar sound of autumn evenings in rural 
places in this country is a chorus of the snowy tree cricket, CEcanthus 
niveus. Very many individuals of this species, in fact all that are 
chirping in any locality, chirp in unison. Early in the evening, when 
the chirping first begins, there may be a lack of unanimity in keeping 
time; but this lasts only for a short period, soon all chirp in unison, 
and the monotonous beat of their call is kept up uninterrupted 
throughout the night. Individual singers will stop to rest, but when 
they start again they keep time with those that have continued the 
chorus. 

Other instances of insect choruses have been recorded. Sharp 
('99, 156) quotes accounts of two produced by ants; one of these is 
given on an earlier page (p. 80). 



CHAPTER III 
THE INTERNAL ANATOMY OF INSECTS 

Before making a more detailed study of the internal anatomy of 
insects, it is well to take a glance at the relative positions of the differ- 
ent systems of organs within the body of insects and other arthropods. 

One of the most striking features in the structure of these animals 
is that the body-wall ser\^es as a skeleton, being hard, and giving sup- 
port to the other organs of the body. This skeleton may be repre- 
sented, therefore, as a hollow cylinder. We have now to consider the 
arrangement and the general form of the organs contained in this 
cylinder. 

The accompanying diagram (Fig. 105), which represents a vertical, 
longitudinal section of the body, will enable the student to gain an 




Fig. 105. — Diagram showing the relations of the internal organs; 
a, alimentary canal; A, heart; w, muscle; n, nervous system; 
r, reproductive organs. 

idea of the relative positions of some of the more important organs. 
The parts shown in the diagram are as follows: The body-wall, or 
skeleton; this is made up of a series of overlapping segments; that 
part of it between the segments is not hardened with chitin, thus 
remaining flexible and allowing for the movements of the body. Just 
within the body-wall, and attached to it, are represented a few of the 
muscles (m) ; it will be seen that these muscles are so arranged that the 
contraction of those on the lower side of the body would bend it down, 
while the contraction of those on the opposite side would act in the 
opposite direction, other muscles not shown in the figure provide 
for movements in other directions. The alimentary canal (a) occupies 
the centre of the body, and extends from one end to the other. The 
heart (/z) is a tube open at both ends, and lying between the alimentary 
canal and the muscles of the back. The central part of the nervous 
system (w) is a series of small masses of nervous matter connected by 

(94) 



THE INTERNAL ANATOMY OF INSECTS 95 

two longitudinal cords: one of these masses, the brain, lies in the 
head above the alimentary canal ; the others are situated, one in each 
segment, between the alimentary canal and the layer of muscles of the 
ventral side of the body; the two cords connecting these masses, or 
ganglia, pass one on each side of the oesophagus to the brain. The 
reproductive organs (r) lie in the cavity of the abdomen and open near 
the caudal end of the body. The respiratory organs are omitted from 
this diagram for the sake of simplicity. We will now pass to a more 
detailed study of the different systems of organs. 



I. THE HYPODERMAL STRUCTURES 

The active living part of the body-wall is the hypodermis, already 
described in the discussion of the external anatomy of insects. In 
addition to the external skeleton, there are derived from the hypo- 
dermis an internal skeleton and several types of glands. 

a, THE INTERNAL SKELETON 

Although the skeleton of an insect is chiefly an external one, there 
are prolongations of it extending into the body-cavity. These 
inwardly directed processes, which serve for the attachment of 
muscles and for the support of other viscera are termed collectively 
the internal skeleton or endo-skeleton. The internal skeleton is much 
more highly developed in adult insects than it is in the immature 
instars. 

Sources of the internal skeleton. — The parts of the internal skele- 
ton are formed in two ways : first by the chitinization of tendons of 
muscles; and second, by invaginations of the body -wall. 

Chitinized tendons. — Chitinized tendons of the muscles that move 
the mouth-parts, of muscles that move the legs, and of other muscles 
are of frequent occurrence. As these chitinized tendons help support 
the internal organs they are considered as a part of the internal 
skeleton. 

Invaginations of the body-wall or apodemes. — The second and more 
important soiu-ce of the parts of the internal skeleton consists of 
invaginations of the body- wall. Such an invagination is termed an 
dpodeme. The more important apodemes, if not all, arise as invagina- 
tions of the body-wall between sclerites or at the edge of a sclerite on 
the margin of a body-segment; although by the fusion of sclerites 
about an apodeme, it may appear to arise from the disc of a sclerite. 



96 



AN INTRODUCTION TO ENTOMOLOGY 




Frequently, in the more generalized insects, the mouth of an apodeme 
remains open in the adult insects. In Figure io6 are represented two 
apodemes that exist in the thorax of a 
locust, Melanoplus. Each of these {ap 
and ap) is an invagination of the body- 
wall, between the epistemimi and the 
epimeron of a segment, immediately 
above the base of a leg. These are known 
as the lateral apodemes of the thorax and 
serve as points of attachment of muscles. 

The number of apodemes may be very ^\,'%^^lt'1l!tL!i. 
large, and it varies greatly in different and metathorax of Melano- 
insects. Among the more important apo- apodemes,^c^^ ap^ 
demes are the following: — 

The tentorium. — The chief part of the internal skeleton of the 
head is termed the tentorium. This was studied by Comstock 
and Kochi ('02). We found that in the generalized insects studied 
by us it is composed of two or three pairs of apodemes that, extend- 
ing far into the head, meet and coalesce. The three pairs of 
apodemes that may enter into the formation of the tentoriimi 
were termed the anterior, the posterior, and the dorsal arms of the 
tentorium respectively. The coalesced and more or less expanded 
tips of these apodemes constitute the body of the tentorium. From 
the body of the tentoritmi there extend a variable munber of processes 
or chitinized tendons. 

The posterior arms of the tentorium. — The posterior arms of the 
tentorium (Fig. 107, 109, no, pt) are the lateral apodemes of the 





Fig. 107. — Tentorium 
of a co::kroach, dor- 
sal aspect. 



Fig. 108.— Part of the 
tentorium of a cric- 
ket, ventral aspect. 



maxillary segment. In many Orthoptera the open mouth of the 
apodeme can be seen on the lateral aspect of the head, jtist above the 



THE INTERNAL ANATOMY OF INSECTS 



97 




Fig. 109. — Head of 
Melajnplus, cau- 
dal aspect. 



articulation of the maxilla (Fig. 48). In the Acridiidae (Fig. 109) 
these apodemes bear a striking resemblance to the lateral apodemes 
of the thorax (Fig. 106), except that the ventral process of the maxil- 
lary apodeme is much more prominent, and the two from the opposite 
sides of the head meet and coalesce, thus forming 
the caudal part of the body of the tentorium. 

The anterior arms of the tentorium. — Each anterior 
arm of the tentorium (Fig. 107, 108, no, at) is an 
invagination of the body-wall which opens on the 
margin of the antecoxal piece of the mandible 
when it is distinct ; if this part is not distinct the 
apodeme opens between the clypeus and the front 
(Fig. 46, at). 

The dorsal arms of the tentorium. — Each dorsal 
arm of the tentorium arises from the side of the 
body of the tentorium between the anterior and posterior arms 
and extends either to the front or to the margin of the antennal 
sclerite (Fig. 107, 108, no, dt). 

The frontal plate of the tentorium. — In the cockroaches the anterior 
arms of the tentorium meet and fuse, forming a broad plate situated 
between the crura cerebri and the mouth ; this plate was termed by 
us the frontal plate of the tentorium (Fig. 107,/^). On each side, an 
extension of this plate connects it with the body of the tentorium; 
these enclose a circular opening through which pass 
the crura cerebri. 

Other cervical apodemes and some chitinized 
tendons are described in the paper cited above. 

The endothorax. — The internal skeleton of the 
thorax is commonly termed the endothorax; under 
this head are not included the internal processes of 
the appendages. 

The endothorax is composed of invaginations of 
each of the sections of a thoracic ring. Those por- 
tions that are derived from tergites are termed 
phragmas; those derived from the pleurites, lateral 
apodemes; and those, from the stemites, furcce. 

The phragmas. — A phragma is a transverse partition extending 
entad from the front or the hind margin of a tergite ; three of them 
are commonly recognized; these were designated by Kirby and 
Spence (1826) the propkragma, the mesophragma, and the meta- 
phragma; but, as they do not arise one from each segment of the 




Fig. I 10. — Ten- 
torium of Mela- 
nopliis, cephalic 
aspect. Thedistal 
end of the dorsal 
arms detached. 



AN INTRODUCTION TO ENTOMOLOGY 




thorax, and arise differently in different insects, these terms are mis- 
leading. No phragma is borne by the prothorax; the mesothorax 
may bear two and the metathorax one, or the mesothorax one and the 

metathorax two. A more definite 

terminology is that used by Snod- 
grass ('09) by which the anterior 
phragma of any segment is termed 
the prephragma of that segment, 
and the posterior phragma of any 
segment is termed the postphragma 
of that segment. 

The lateral apodemes. — Each lat- 
eral apodeme is an invagination of 
the body-wall between the epister- 
num and the epimeron. The lateral apodemes are referred to above 
(Fig. 106). 

ThefurccB. — Each fiu*ca is an invagination of the body-wall arising 
between the sternum and the stemellimi (Fig. 1 1 1) ; when the sternel- 
lum is obsolete, as it is in most insects, the furca arises at the caudal 
margin of the segment (Fig. 112). 



Pig. Ill . — Ventral aspect of the 
metathorax of Stenopelmatus. 
The _ position of the furca 
within the body is represented 
by a dotted line. 



h. THE HYPODERMAL GLANDS 

A gland is an organ that pDssesses the function of either trans- 
forming nutritive substances, which it derives from the blood, into 
some useful substance, as mucus, wax, or venom, or of assimilating 
and removing from the body waste 
material. 

The different glands vary greatly in 
structure; many are unicellular, the 
gland consisting of a single cell, which 
differs from the other cells of the epithe- 
lium of which it is a part in being larger 
and in possessing the secreting and ex- 
creting functions; others are multicel- 
lular, consisting of more than one cell. Fig. 112.— Ventral aspect of the 
usually of many cells. In these cases ^^^^fhepo^tfordthl 
the glandular area usually becomes furcae wit'iin the body are 
invaginated, and provided with an indicated by dotted lines, 
efferent duct; and often the invagination is much branched. 

The glands found in the body of an insect can be grouped under 
three heads; the hypodermal glands, the glands of the alimentary 




THE INTERNAL ANATOMY OF INSECTS 




canal, and the glands of the reproductive organs. In this place 
reference is made only to the hypodermal glands, those developed 
from the hypodermis. 

The Molting-fluid glands. — Under this 
head are classed those unicellular, h^/po- 
dermal glands that secrete a fluid that 
facilitates the process of molting, as des- 
cribed in the next chapter (Fig. 113). 

While molting-fluid glands are very 
numerous and conspicuous in certain 
insects, those living freely exposed where 
there exists the greatest liability to rapid 
Fig. 113. — Molting-fluid glands desiccation, Tower ('06) states that he 

of the last larvalinstar of j^as never found these glands in larva 

Leptinolarsa dectmhtieata , ]ust ° 

before pupation; le, larval that live m burrows, or m the soil, or in 

epidermis; Id larval dermis; ^ells; in these cases the molting fluid is 

ot/, moltmg fluid; ^e, formmg , , , r 

pupal epidermis; h, hypoder- apparently secreted by the entire hypo- 

?lt= S'^"^°l^^"g fl^i^ gl^'^^ dermal layer. 

(After Tower). ^, , , . , 

Glands connected with setae. — There 

are in insects several kinds of glands in which the outlet of the gland 
is through the limien of a seta. The function of the excretions of 
these glands is various as indicated 
below. There are also differences in 
the manner of issuance of the excre- 
tion from the seta. In some cases, as 
in the tenent hairs on the feet of certain 
insects, the excretion can be seen to 
issue through a pore at the tip of the 
seta. In some kinds of venomous setag 
the tip of the seta breaks off in the 
wound made by it and thus sets free 
the venom. But in most cases the 
manner of issuance has not been deter- 
mined, although it is commonly believed 
to be by means of a minute pore or 
pores in the seta, the thickness of the 
wall of the seta making it improbable 
that the excretion passes from the seta 
by osmosis. 

The structure of a glandular seta 
is illustrated by Figure 114; the 
essential difference between such a seta and an ordinary one, that is a 




Fig. 114. — Glandular s^ta; 5, seta; 
c, cuticula; h, hypodermis; bm, 
basement membrane; tr, tricho- 
gen; g, gland (After Holmgren). 



100 



AN INTRODUCTION TO ENTOMOLOGY 



clothing hair, is that there is connected with it, in addition to the 
trichogen cell which produced it, the gland cell which opens through it. 
In most of the published figures of glandular setae there is no indi- 
cation that these organs are supplied with nerves ; but in some cases 
a nerve extending to the gland cell is clearly shown. This condition 
may be found to be general when more extended investigations of 
glandular cells have been made. The best known kinds of glandular 
setce are the following : 

Venomous setce and spines. — These are best known in larvae of 
Lepidoptera, several common species of which possess stinging hairs; 
among these are Lagoa crispata, Sihine stimulea, Automeris to, and 
the brown-tail moth, Euproctis chrysorrhcea. 

Androconia. — The term androconia* is applied to some peculiarly 
modified scales on the wings of certain male butterflies. These are 
the outlets of glands, which secrete a fluid with an agreeable odor; 
the supposed function of which is to attract the opposite sex, like the 
beautiful pltimage and songs of male birds. The androconia differ 
marvelously from ordinary scales in the 
variety of their forms (Fig. 115). They 
usually occur in patches on the upper sur- 
face of the fore wings; and are usually 
concealed by other scales; but they are 
scattered in some butterflies. The most 
familiar examples of grouped androconia 
are those that occur in the discal stigma of 
the hair-streaks, in the brand of certain 
skippers and in the costal fold of others, 
and in the scent-pouch of the male of the 
monarch butterfly 

The specific scent-glands of females. — 
The well-known fact that if an unfertilized 
female moth be confined in a cage or 
otherwise in the open many males of the 

Fig._ 115.— Androconia from the same species as the female will be attracted 
wmgsof male butterflies (After . ^ . .. , . 

Kellogg). to it, and sometimes evidently from a great 

distance, leads to the conclusion that there 

must emanate from the female a specific odor. The special glands 

producing this odor have not been recognized. 

Tenent hairs. — In many insects the pulvilli or the empodia are 

clothed with numerous hairs that are the outlets of glands which 



I 

I 

I 




^Androconia: andro- {dvT/jp,dpdp6s), male; conia (xoi'ia), dust. 



THE INTERNAL ANATOMY OF INSECTS 



101 



secrete ai adhesive fluid ; this enables the insect to walk on the lower 
surface of objects (Fig. ii6). 




Fig. Ii6. — A, terminal part of a tenent hair from Eupolus, showing canal in the 
hair and opeaing near the tip; B, cross-section throu.^h a tarsal segment of 
Telephorus; c, cuticula; g, gland of tenent hair; h, h, tactile hairs; hy, hypo- 
dermis; n, nerve; s, sense-cell of tactile hair; t, t, tenent hairs (After Dewitz). 

The osmeteria. — In many insects there are hypodermal glands that 
open into sac-like invaginations of the body- wall which can be 
evaginated when the insect wishes to make use of the secretion pro- 
duced by these glands; such an organ i§ termed an osmeterium. The 
invagination of the osmeterium admits of an accumulation of the 
products of the gland within the cavity of the sac thus formed; when 
the osmeterium is evaginated the secretion becomes exposed to the air, 
being then on the outside of the osmeterium, and rapid diffusion of 
the secretion results. 

The most familiar examples of osmeteria are those of the larvas 
of the swallow-tailed butterflies, which are forked, and are thrust out 
from the upper part of the prothorax when the caterpillar is disturbed, 

and which 
diffuse a dis- 
agreeable odor 
(Fig. 117). 
They are ob- 
viously organs 
of defense. 
Osmeteria 

are present in the larvae of certain blue butterflies, Lycaenidce. These 
are in the seventh and eighth abdominal segments, and secrete a 
honey-dew, which attracts ants that attend and probably protect 
the larvae. The osmeteria of many other caterpillars have been 
described. 




Fig. 117 — Larva of Papilio thoas; 0, osmeterium expanded. 



102 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. IT 8. — Wax-plates of Lhe honeybee 
(After Cheshire). 



Glands opening on the surface of the body. — There are several 
kinds of hypodermal glands, differing widely in function, that open 
on the surface of the body; among the best known of these are the 
following : 

Wax-glands. — The worker honeybee has fotn* pairs of wax-glands; 
these are situated on the ventral wall of the second, third, fourth, and 
fifth abdominal segments, and on that part of the segment which is 
overlapped by the preceding segment; each gland is simply a disc- 
like area of the hypodermis 
(Fig. 1 1 8). The cuticle 
covering each gland is 
smooth and delicate, and is 
known as a wax plate. 
The wax exudes through 
these plates and accumu- 
lates, forming little scales, 
which are used in making 
the honey-comb. 

Wax -glands exist in 
many of the Homoptera. In some of these the unicellular wax- 
glands are distributed nearly all over the body; and the product 
of these glands forms, in some, a powdery covering; in others, 
a clothing of threads; and in still others a series of plates (Fig. 119). 
Certain coccids excrete wax in con- 
siderable quantities. China wax, which 
was formerly an article of commerce, 
is the excretion of a coccid known as 
Pe-la (Ericerus Pe-la). 

Froth-glands of spittle-insects. — In 
the spittle-insects (Cercopidcc) there 
are large hypodermal glands in the 
pleural regions of the seventh and eighth 
abdominal segments, which open 
through numerous minute pores in the 
cuticula. These glands secrete a muci- 
laginous substance, which is mixed with 
a fluid excreted from the anus, and thus 
fits it for the retention of bubbles of air 
included in it by means of abdominal appendages (Guilbeau '08). 

Stink-glands. — Glands that secrete a liquid having a fetid odor and 
that are doubtless defensive exist in many insects. In the stink-bugs 




Fig. 119. — Orthcsia, greatly en- 
larged. 



THE INTERNAL ANATOMY OF INSECTS 



103 



(PentatoniicUe) the fluid is excreted through two openings, one on each 
side of the lower side of the body near the middle coxse ; in the bed- 
bug (Cimcx), the stink-glands open in the dorsal wall of the first three 
abdominal segments ; in Dytiscus, the glands open on the prothorax ; 
and in certain Coleoptera they open near the caudal end of the bodv. 
These are merely a few examples of the many glands of this type that 
are known. 

The cephalic silk-glaiids. — In the Lepidoptera, Trichoptera, and 
Hymenoptera, there is a pair of glands that secrete silk, and which 
open through the lower lip. These glands are designated as the 
cephalic silk-glands to distinguish them from the silk-glands of certain 
Neuroptera and Coleoptera in which the silk is produced by modified 
Malpighian vessels and is spun from the anus. 

The cephalic silk-glands are elongate and coiled ; they often 
extend nearly the whole length of the body ; the two ducts unite and 
the single terminal duct opens through the lower lip, and is not 
connected with the mouth cavity. These glands are a pair of 

salivary glands which have 
been transformed into silk 
organs. According to Carriere 





Fig. 1 20. — The salivary glands 
of the honeybee (After 
Cheshire). 



Fig. 121. — Theman- 
viibular gland of a 
honeybee. 



and Burger ('97), who studied their development in the embryo 
of a bee, they are developed from the rudiments of the spiracles 
of the first thoracic segment. In the later development they move 



104 AN INTRODUCTION TO ENTOMOLOGY 

cephalad and the paired openings become a single one. This is the 
reason that in the adult there are no spiracles in the prothorax. 

The Salivary glands. — The term saUvary glands is a general one, 
applied to various glands opening in the vicinity of the mouth. The 
number of these varies greatly in different insects; the maximum 
number is found in the Hymenoptera. In the adult worker honey- 
bee, for example, there are four pairs of glands opening into the 
mouth; three of these are represented in Figure 120 and the fourth 
in Figure 121. These are designated as the supracerebral glands 
(Fig. 120, j), the postcerebral glands (Fig. 120, 2), the thoracic 
glands (Fig. 120, 3), and the mandibulary glands (Fig. 121), 
respectively. 

II. THE MUSCLES 

There exist in insects a wonderfully large number of muscles; 
some of these move the segments of the body, others move the appen- 
dages of the body, and still others are found in the viscera. Those 
of the viscera are described later in the accounts of the organs in 
which they occur. 

The muscles that move the segments of the body form several 
layers just within the body-wall, to which thsy are attached. The 
inner layer of these is well shown in Figure 122, which is a copy of 
one of the plates in the great work by Lyonet (1762) on the anatomy 
of a caterpillar, Cossus ligniperda. The two figures on this plate 
represent two larvae which have been split open lengthwise, one on the 
middle line of the back (Fig. 5), and one on the middle line of the 
ventral surface (Fig. 4) ; in each case the alimentary canal has been 
removed, so that only those organs that are attached quite closely to 
the body-wall are left. The bands of parallel fibers are the muscles 
that move the segments. It should be borne in mind, however, that 
only a single layer of muscles is represented in these figures, the layer 
that would be seen if a caterpillar were opened in the way indicated. 
When these muscles are cut away many other muscles are found 
extending obliquely in various directions between these muscles and 
the body-wall. 

In the head and thorax of adult insects the arrangement of the 
muscles is even more complicated ; for here the muscles that move the 
appendages add to the complexity of the muscular system. 

As a rule, the muscles of insects are composed of many distinct 
fibers, which are not enclosed in tendinous sheaths as with Verte- 



THE INTERNAL ANATOMY OF INSECTS 



105 




r 









mmii 



Fig. 122. — Internal anatomy of a caterpillar, Cossus ligniperda; i, principal 
longitudinal trachce; 2, central nervous system; j, aorta; 4, longitudinal 
dorsal muscles; 5, longtiudinal ventral muscles; 6, wings of the heart; 7, 
tracheal trunks arising near the spiracles; 8, reproductive organs; 9, vertical 
muscles; 10, last abdominal ganglion (From Lyonet). 



106 A N INTROD UCTION TO ENTOMOLOG Y 



are lurnisnea witn a tendon at tne end 



brates. But the muscles that move the appendages of the body- 
are furnished with a tendon at the end farthest from the body 

(Fig- 123). 

The muscles of in- 
sects appear very differ- 
ently from those of Ver- 
tebrates. In insects, the 
Fig. 123— A leg of a May-beetle (After Straus- muscles are either Color- 
Durckheim). l^^g ^^^ transparent, or 

yellowish white ; and they are soft, almost of a gelatinous consistency ; 
notwithstanding this they are very efficient. The fibers of insect 
muscles are usually, if not always, of the striated type. 

Much has been written regarding the muscular power of insects, 
which has been supposed to be extraordinarily great; the power of 
leaping possessed by many and the great loads, compared to the 
weight of the body of the insect, that insects have drawn when 
harnessed to them by experimenters, have been cited as illustrating 
this. But it has been pointed out that these conclusions are not 
warranted; that the comparative contractile force of muscles of the 
same kind depends on the number and thickness of the fibers, that is, 
on the comparative areas of the cross-sections of the muscles com- 
pared ; that this sectional area increases as the square of any linear 
dimension, while the weight of similar bodies increases as the cube of 
any linear dimension; and consequently, that the muscles of the legs 
of an insect one fourth inch long and supporting a load 399 times its 
own weight, would be subjected to the same stress, per square inch of 
cross-section, as they would be in an insect 100 inches long of precisely 
similar shape, that carried only its own weight. We thus see that it is 
the small size of insects rather than an unusual strength of their 
muscles, that makes possible the apparently marvelous exhibitions of 
muscular power. 

Detailed accounts of the arrangement of the muscles in particular 
insects have been published by various writers: among the more 
important of these monographs are the following Lyonet (1762), 
on the larva of a cossid moth; Straus-Durckheim (1828), on a May- 
beetle; Newport (1839), on the larva of a Sphinx moth; Lubbock 
(1858), on the larva Pygaera bucephala; Berlese ('09a), on several 
insects; and Forbes ('14) on caterpillars. 



THE INTERNAL ANATOMY OF INSECTS 107 

III. THE ALIMENTARY CANAL AND ITS APPENDAGES 

a. THE MORE GENERAL FEATURES 

The alimentary canal is a tube extending from one end of the body 
to the other. In some larvee, its length is about the same as that of 
the body; in this case it extends in a nearly straight line, occupying 




a iivnnsa 



Fig. 124. — Internal anatomy of a cockroach, Periplanela orientalis; a, antennas; 
bi, ^2, 63, first, second, and third legs; c, cerci: d, ventricular ganglion; e, 
salivary duct; f, salivary bladder, g, gizzard or proventriculus ; h, hepatic 
coeca; i, mid-intestine; j, Malpighian vessels; k, small intestine; /, large 
intestine: m, rectum; », first abdominal ganglion; 0, ovary; p, sebaceous 
glands (From RoUeston). 



108 AN INTRODUCTION TO ENTOMOLOGY 

the longitudinal axis of the body, as is represented in the diagram 
given above (Fig. 105). In most insects, however, it is longer than 
the body, and is consequently more or less convoluted (Fig. 124); 
great variations exist in the length of the alimentary canal as com- 
pared to the length of the body; it is longer in herbivorous insects 
than it is in those that are carnivorous. 

The principal divisions. — Three chief divisions of the alimentary- 
canal are recognized ; these are termed the fore-intestine, the mid- 
intestine, and the hind-intestine, respectively. In the embryological 
development of the alimentary canal, the fore-intestine and the hind- 
intestine each arises as an invagination of the ectoderm, the germ 
layer from which the hypodermis of the body- wall is derived (p. 29). 
The invagination at the anterior end of the body, which develops 
into the fore-intestine, is termed the stomodceum; that at the posterior 
end, which develops into the hind-intestine, the proctodceum. Between 
these two deep invaginations of the outer germ layer of the embryo, 
the stomodffitmi and the proctodaeum, and ultimately connecting 
them, there is developed an entodermal tube, the mesenteron, which 
becomes the mid-intestine. 

These embryological facts are briefly stated here merely to 
elucidate two important features of the alimentary canal : first, the 
fore-intestine and the hind-intestine are invaginations of the body 
wall and consequently resemble it in structure, the chitinous lining of 
these two parts of the alimentary canal is directly continuous with 
the cuticula of the body wall, and the epithelium of these two parts 
and the hypodermis are also directly continuous; and second, the 
striking differences, pointed out later, in the structure of the mid- 
intestine from that of the fore- and hind-intestines are not surprising 
when the differences in origin are considered. 

Imperforate intestines in the larvae of certain insects. — ^Inthelarvse 
of certain insects the lumen of the alimentary canal is not a continuous 
passage; in these larvse, while food passes freely from the fore- 
intestine to the mid-intestine, there is no passage of the waste from 
the mid-intestine to the hind-intestine; there being a constriction at 
the point where the mid-intestine and hind-intestine join, v/hich 
closes the passage during a part or the whole of the larval life. This 
condition has been observed in the following families: — 

(a) Hymenoptera. — Proctotrypidag (in the first larval instar), 
Ichneumonidee, Formicidae, Vespidac, and Apidas. 

{b) Diptera. — Hippoboscidse. 



THE INTERNAL ANATOMY OF INSECTS 



109 



(c) Neuroptera. — Myrmeleonidce, Osmylidae, Sisyridce, and 
Chrysopidas. In these families the larvas spin silk from the anus. 

{d) Coleoptera. — In the Campodeiform larvse of Stylopidse and 
Meloidce. 

b. THE FORE-INTESTINE 

The layers of the fore-intestine. — The following layers have been 
recognized in the fore-intestine : 

The intima. — This is a chitinous layer which lines the cavity of 
the fore-intestine; it is directly continuous with the cuticula of the 
body-wall ; and is molted with the cuticula when this is molted. 

The epithelium. — This is a cell layer which is continuous with the 
h37podermis; it is sometimes quite delicate so that it is difficult to 
demonstrate it. 

The basement membrane. — Like the hypodermis the epitheliimi is 
bounded on one side by a chitinous layer and on the other by a base- 
ment membrane. 

The longitudinal ynuscles. — Next to the basement membrane there 

is a layer of longitudinal muscles. 
The circular muscles. — Out- 
side of the longitudinal muscles 
there is a layer of circular 
muscles. 

The peritoneal membrane. — 
Surrounding the alimentary 
canal there is a coat of con- 
nective tissue, which is termed 
the peritoneal membrane. This 
is one of a few places in which 
connective tissue, so abundant 
in Vertebrates, is found in in- 
sects. 

The regions of the fore- 
intestine. — Several distinct reg- 
ions of the fore-intestine are 
recognized; but the extent of 
these regions differ greatly in 
different insects. 

The pharynx. — The phar3mx 

is not a well-defined region of the 

intestine ; the term pharynx is commonly applied to a region between 

the mouth and the oesophagus; in mandibulate insects the pharynx 




Fig. 125. — Longitudinal section through 
the head of A nosa ptexippns, showing 
the interior of the left half; mx, left 
maxilla, the canal of which leads into the 
pharynx; ph, pharynx; 0, oesophagus; 
m, m, muscles of the pharynx; sd, 
salivary duct (After Burges). 



no 



AN INTRODUCTION TO ENTOMOLOGY 



is not distinct from the mouth-cavity; but in sucking insects the 
pharynx is a highly speciaHzed organ, being greatly enlarged, muscu- 
lar, and attached to the wall of the head by muscles. It is the pump- 
ing organ by which the liquid food is drawn into the alimentary canal. 
The pharnyx of the milkweed butterfly (Fig. 125) is a good example 
of this type of pharynx. 

The oesophagMS. — The oeso- 
phagus is a simple tube which 
traverses the caudal part of the 
head and the cephalic part of the 
thorax. There are variations in 
the application of the term 
oesophagus depending on the 
presence or absence of a crop 
and of a proventriculus, which 
are modified portions of the 
oesophagus; when either or both 
of these are present, the term 
oesophagus is commonly restricted 
to the unmodified part ot the 
fore-intestine. 

The crop. — In many insects a 
portion of the oesophagus is dilated 
and serves as a reservoir of food ; 
this expanded part, when present, 
is termed the crop. In the cock- 
roach (Fig. 124) it is very large, 
comprising the greater part of the 
fore-intestine ; in the ground-beetle 
Carabus (Fig. 126, c), it is much 
more restricted; this is the case 
also in the honeybee, where it is 
a nearly spherical sac in which 
the nectar is stored as it is col- 
lected from flowers and carried to 
the hive. In some insects the 
crop is a lateral dilatation of the 
oesophagus, and in some of these 
it is stalked. 

The proventriculus. — In certain insects that feed on hard sub- 
stances, the terminal portion of the fore-intestine, that part im- 




Fig. 126. — ^Alimentary canal oi Carabus 
auralus; h, head; oe, oesophagus; c, 
crop; pv, proventriculus; mi, mid- 
intestine covered with viiUform gastric 
cceca; mv, Malpighian vessels; hi, part 
of hind-intestine; r, rectum; ag, anal 
glands; mr, muscular reservoir (After 
Dufour). 



THE INTERNAL ANATOMY OF INSECTS 



111 




Fig. 127. — Cross-section of the 
proventriculus of a larva of 
Corydalus. 



mediately in front of the mid-intestine or ventriculus, is a highly 
speciaHzed organ in which the food is prepared for entrance into 
the more delicate ventriculus ; such an 
organ is termed the proventriculus (Fig. 
126, pv). The characteristic features 
of a proventriculus are a remarkable 
development of the chitinous mtima 
into folds and teeth and a great in- 
crease in the size of the muscles of this 
region. The details of the structure 
of this organ vary greatly in different 
insects; a cross-section of the proven- 
triculus of the larva of Corydalus (Fig. 
127) will serve to illustrate its form. 
In the proventriculus, the food is both 
masticated and more thoroughly 
mixed with the digestive fluids. 

The oesophageal valve.—Wh&n the 
fore-intestine projects into the mid- 
intestine, as shown in Figure 128, 
the folded end of the fore-intestine 
is termed the (esophageal valve. 



C. THE MID-INTESTINE 

The mid-intestine is the inter- 
mediate of the three principal 
divisions of the alimentary canal, 
which are distinguished by differ- 
ences in their embryological origins, 
as stated above. The mid-intestine 
is termed by different writers the 
mese liter on, the stomach, the chylific 
ventricle, the chyle stomach, and the 
ventriculus. 

The layers of the mid-intestine. — 
The structure of the mid-intestine 
differs markedly from that of the 
fore-intestine. In the mid-intestine 
there is no chitinous intima, and the 
relative positions of the circular and 
longitudinal muscles are reversed. 




Fig. 128. — The cesophageal valve of a 
larva of Simulium; F, fore-intestine: 
M, mid-intestine; u, point of uriion 
of fore-intestine and mid-intestiner 
p, peritoneal membrane; i, 
intima of fore- intestine; e, epithe- 
Hum of fore-intestine; pt, peritrophic 
membrane; m, muscles. 



112 



AN INTRODUCTION TO ENTOMOLOGY 



The sequence of the different layers is as follows : a lining epithelium, 
which is supported by a basement membrane, a layer of circular 
muscles, a layer of longitudinal muscles, and a peritoneal membrane. 

The epithelium. — The epitheliiun of the mid-intestine is very con- 
spicuous, being composed of large cells, which secrete a digestive fluid. 
These cells break when they discharge their secretion and are replaced 
by new cells, which are developed in centers termed nidi (Fig. 129, w). 
The extent of the digestive epithelium is increased in many insects 
by the development of pouch-like diverticula of the mid-intestine, 
these are the gastric cceca (Fig. 124, h). These differ greatly in niun- 
ber in different insects and are wanting in some. In some predaceous 
beetles they are villiform and very numerous (Fig. 126, mi). 

The peritrophic membrane. 
■ — In many insects there is a 
membranous tube which is form- 
ed at or near the point of union of 
the fore-intestine and the mid- 
intestine and which incloses the 
food so that it does not come in 
contact with the delicate epithe- 
lium of the mid-intestine; this is 
known as the peritrophic mem- 
brane (Fig. 128, pt). As a rule 
this membrane is found in insects 
that eat solid food and is lacking 
in those that eat liquid food. It 
is obvious that the digestive fluid 
and the products of digestion 
pass through this membrane. It 
is continuously formed at its 
point of origin and passes from 
the body inclosing the excrement. 

d. THE HIND-INTESTINE 

The layers cf the hind-intes- 
tine. — The layers of the hind-in- 
testine are the same as those of 
the fore-intestine described 
above, except that a greater or 
less number of circular muscles exist between the basement membrane 
of the eoithelial layer and the layer of longitudinal muscles. The 




129. — Resting epitheHum of mid- 
Intestine of a dragon-fly naiad; b, 
bases of large cells filled with digestive 
fluid; cm, space filled by circular mus- 
cles, /m . longitudinal muscles ; «, nidus 
in which new cells are developing (From 
Needham). 



THE INTERNAL ANATOMY OF INSECTS 113 

sequence of the layers of the hind-intestine is, therefore, as follows: 
the intima, the epithelium, the basement membrane, the ental circular 
muscles, the longitudinal muscles, the ecial circular muscles, and the 
peritoneal membrane. 

The regions of the hind-intestine. — Three distinct regions are 
commonly recognized in the hind-intestine, these are the small intestine 
(Fig. 124, k), the large intestine (Fig. 124, /), and the rectum (Fig. 
124, w). 

The Malpighian vessels.^ — There open into the beginning of the 
hind-intestine two or more simple or branched tubes (Fig. 124, ;), 
these are the Malpighian vessels. The number of these vessels varies 
in different insects but is very constant within groups; there are 
either two, four, or six of them; but, as a result of branching, there 
may appear to be one hundred or more. The function of the Mal- 
pighian vessels has been much discussed ; it was formerly believed to 
be hepatic, but now it is known that normally it is urinary. 

The Malpighian vessels as silk-glands. — There are certain larvas 
that in making their cocoons spin the silk used from the anus. These 
larvas are chiefly found among those in which the passage from the 
mid-intestine to the hind-intestine is closed. The silk spun from the 
anus is secreted by the Malpighian vessels. 

Among the larvag in which the Malpighian vessels are known to 
secrete silk are those of the Myrmeleonidas, Osmylus (Hagen 1852), 
Sisyra (Anthony '02), Lebia scapularis (Silvestri '05), and the 
Coccidag (Berlese '96). Berlese states that the Malpighian vessels 
secrete the woof of the scale of the Coccidas. 

The caecum. — In some insects there is a pouch-like diverticulum 
of the rectum, this is the ccecum. 

The anus. — The posterior opening of the alimentary canal, the 
anus, is situated at the caudal end of the abdomen. 

IV. THE RESPIRATORY SYSTEM 

Insects breathe by means of a system of air-tubes, which ramify 
in all parts of the body and its appendages ; these air-tubes are of two 
kinds, which are termed irachece and tracheoles, respectively. In 
adult insects and in most nymphs and larvce, the air is received 
through openings in the sides of the segments of the body, which are 
known as spiracles or stigmata. 

Many insects that live in water are furnished with special devices 
for obtaining air from above the water; but with naiads and a few 



114 



AN INTRODUCTION TO ENTOMOLOGY 



aquatic larv^ the spiracles are closed; in these insects the air is 
purified by means of gill-like organs, termed tracheal gills. A few 
insects have blood-gills. 

Two types of respiratory systems, therefore, can be recognized: 
first, the open type, in which the air is received through spiracles ; and 
second, the closed type, in which the spiracles are not functional. 

a. THE OPEN OR HOLOPNEUSTIC TYPE OR RESPIRATORY ORGANS 

That form of respiratory organs in which the trachae communicate 
freely with the air outside the body through open spiracles is termed 
the open or holopneustic type.* 

As the open type of respiratory organs is the most common one, 
those features that are common to both types will be discussed under 
this head as well as those that are peculiar to this type. Under the 
head of closed respiratory organs will be discussed only those features 
distinctly characteristic of that type. 



/. The Spiracles 

The position of the spiracles. — The spiracles are situated one on 
each side of the segments that bear them or are situated on the lateral 
aspects of the body in the transverse conjunctivae. 

The question of the position of the spiracles has not been thor- 
oughly investigated ; but I believe that normally the tracheae, of which 




Pig. 130. — Lateral view of a silk worm showing the spiracles 
(After Verson). 

i:he spiracles are the mouths, are invaginations of the transverse 
conjunctivae between segments. From this normal position a spiracle 
may migrate either forward or backward upon an adjacent segment 
(Fig. 130). 

The number of spiracles. — The normal number of spiracles is ten 
pairs; when in their normal position, there is a pair in front of the 



^Holopneustic: holo (5Xos), whole; pneuma {/rveOna), breath. 



THE INTERNAL ANATOMY OF INSECTS 115 

second and third thoracic segments and the first to the eighth abdom- 
inal segments, respectively. There are none in the corresponding 
position in front of the first thoracic segment. See account of 
cephaHc silk-glands p. 103. 

The two pairs of thoracic spiracles are commonly distinguished as 
the mesothoracic and the metathoracic spiracles ; that is each pair of 
spiracles is attributed to the segment in front of which it is normally 
situated. Following this terminology there are no prothoracic 
spiracles; although sometimes the first pair of spiracles is situated in 
the hind margin of the prothorax, having migrated forward from its 
normal position. It would be better to designate the thoracic 
spiracles as the first and second pairs of thoracic spiracles, respec- 
tively; in this way the same term would be applied to a pair of 
spiracles whatever its position. There are many references in 
entomological works to "prothoracic spiracles," but these refer to the 
pair of spiracles that are more commonly designated the mesothoracic 
spiracles. 

In many cases the abdominal spiracles have migrated back upon 
the segment in front of which they are normally situated, being fre- 
quently situated upon the middle of the segment. 

The statements made above refer to the normal number and dis- 
tribution of spiracles; but a very wide range of variations from this 
type exists. Perhaps the most abnormal condition is that found in 
the genus Smi nthurus of the Collembola, where there is a single pair 
of spiracles which is borne by the neck. In the Podurid^, also of the 
Collembola, the respiratory system has been lost, there being neither 
tracheas nor spiracles. 

Terms indicating the distribution of the spiracles. — The following 
terms are used for indicating the distribution of the spiracles; they 
have been used most frequently in descriptions of lan^as of Diptera. 
These terms were formed by combining with pneustic (from pneo, to 
breathe) the following prefixes: peri-, around, about; pro-, before; 
meta- after; and aniphi, both. 

Peripneustic. — Having spiracles in a row on each side of the body, 
the normal type. 

Propneustic. — ^With only the first pair of spiracles. 

Metapneustic. — With only the last pair of spiracles. 

Amphipneustic. — With a pair of spiracles at each end of the body. 



116 



AN INTRODUCTION TO ENTOMOLOG\ 





a 



Fig. 13 



Spiracles; a, of the larva of 
Corydalus; b, of the larva of Droso- 
phila amcena. 



The Structure of spiracles. — In their simplest form the spiracles or 
stigmata are small round or oval openings in the body-wall. In many- 
cases they are provided with hairs to exclude dust; in some, as in the 

larva of Corydalus, each spiracle is 
furnished with a lid (Fig. 131, a); 
in fact, very many forms of 
spiracles exist. Usually each spir- 
acle opens by a single aperture; 
but in some larvas and pupae of 
Diptera they have several openings 
(Fig. 131, &)■ 

The closing apparatus of the 
tracheae. — Within the body, a 
short distance back of the spiracle, 
there is an apparatus consisting of 
several chitinous parts, surrounding the trachea, and moved by a 
muscle, by which the trachea can be closed by compression (Fig. 132). 
This is the closing apparatus of the trachea. The closing of this appara- 
tus and the 
contraction of 
the body by 
the respiratory 
muscles is sup- 
posed to force 
the air into 
thetracheoles, 
which are the 
essential res- 
piratory or- 
gans. 




Fig. I -52. — -Diagrams representing the closing apparatus of the 
trache.-p; a, b, c, chitinous parts of the apparatus; m, muscle; 
A, apparatus open; B, apparatus closed; C, spiracle and 
trunk of trachea showing the position of the apparatus. 
(From Judeich and Nitsche). 



2. THE TRACHEA • 

Each spiracle is the opening of an air-tube or trachea. The main 
tracheal trunk which arises from the spiracle soon divides into several 
branches, these in turn divide, and by repeated divisions an immense 
number of branches are formed. Every part of the Dody is supplied 
with tracheae. 

In a few insects the group of tracheee arising from a spiracle is not 
connected with the groups arising from other spiracles; this is the 
case in Machilis (Fig. 133). In most insects, however, each group of 
tracheae is connected with the corresponding groups in adiacent seg- 



THE INTERNAL ANATOMY OF INSECTS 117 

ments by one or more longitudinal tracheas, and is also connected 




Fig. 133. — The trachcce of Machilis (From Oudemans). 

with the group on the opposite side of the same segment by one or 
more transverse trachese (Fig. 134). 

The structure of the tracheae. — The fact that 
in their embryological development the tracheas 
arise as invaginations of the body-wall, makes it 
easy to understand the structure of the tracheas. 
The three layers of the body-wall are directly 
continuous with corresponding layers in the wall 
of a trachea (Fig. 135). These layers of -a 
trachea are designated as the intima, the epithe- 
lium, and the basement membrane. 

The mtima is the chitinous inner layer of the 
trachese. It is directly continuous with the 
cuticula of the body- 
wall, and like the 
cuticula is molted at 
each ecdysis. 

A peculiar feature 
of the intima of 
trachea is the fact 
that it is furnished 
with thickenings 
which extend spirally. 
These give the 
1 34-— Larva of tracheae their charac- Fig. 135.— Section of a ixachea 





teristic transversely ^",<^ ^^^f body-v/all; c, 



Cantharis vesicatorta, 
showing the distribu- 
tion of tracheae (From striated appearance. 

the larger trachea be 
pulled apart the intima will tear between the folds of the spiral 
thickening, and the latter will uncoil from within the trachea like a 



basement membrane; sp, 
spiral thickening of the in- 
tima, the tasnidium. 



118 AN INTRODUCTION TO ENTOMOLOGY 

thread (Fig. 135). The spiral thickening of the intima of a trachea is 
termed the tcBrndium. In some insects there are several parallel 
tasnidia; so that when an attempt is made to uncoil the thread a 
ribbon-like band is produced, composed of several parallel threads. 
This condition exists in the larger tracheae of the larva Corydalus. 

The epithelium of the trachea is a cellular layer, which is directly- 
continuous with the hypodermis of the body-wall. 

The basement membrane is a delicate layer, which supports the 
epitheliinn, as the basement membrane of the body-wall supports the 
hypodermis. 

3. The Tracheoles 

The tracheoles are minute tubes that are connected with the tips 
of trachea or arise from their sides, but which differ from trachese in 
their appearance, structure, and mode of origin; they are not small 
tracheae, but structures that differ both histologically and in their 
origin from tracheae. 

The tracheoles are exceedingly slender, measuring less than one 
micron in diameter; ordinarily they do not taper as do trachese; 
they contain no tsenidia; and they rarely branch, but often anasto- 
mose which gives them a branched appearance (Fig. 136, t and 
138 B, /)• 

Each tracheole is of unicellular origin, and is, at first, intracellular 
in position, being developed coiled within a single cell of the epithelium 
of a trachea. In this stage of its development it has no connection 
with the liunen of the trachea in the wall of which it is developing, 
being separated from it by the intima of the trachea. A subsequent 
molting of the intimia of the trachea opens a connection between the 
lumen of the tracheole and the trachea. At the same time or a little 
later the tracheole breaks forth from its mother cell, uncoils, and 
extends far beyond the cell in which it was developed. 

The tracheoles are probably the essential organs of respiration, the 
trachea acting merely as conduits of air to the tracheoles. 

4. The Air-Sacs 

In many winged insects there are expansions of the tracheae, 
which are termed air-sacs. These vary greatly in nimiber and size. 
In the honeybee there are two large air-sacs which occupy a consider- 
able part of the abdominal cavity; while in a May-beetle there are 
hundreds cf small air-sacs. The air-sacs differ from tracheae in 
lacking tanidia. 



THE INTERNAL ANATOMY OF INSECTS 



119 



As the air-sacs lessen the specific gravity of the insect they proba- 
bly aid in flight ; as filling the lungs with air makes it easier for a man 
to float in water ; in each case there is a greater volimie for the same 
weight. 

5. Modifications of the open type of respiratory organs in 
aquatic insects 

There are many insects in which the spiracles are open that live in 
water ; these insects breathe air obtained from above the surface of 
the water. Some of these insects breathe at the surface of the water, 




Fig. 136. — Part of a tracheal gill of the larva of Corydalus; T, trachea; t, 
tracheoles. 

as the larvcB and pupae of mosquitoes, the larvae of Eristalis, and the 
Nepidse; others get a supply of air and carry it about with them 
beneath the surface of the water, as the Dytiscidae, the Notonectidae 
and the Corisidae. The methods of respiration of these and of other 
aquatic insects with open spiracles are described in the accounts of 
these insects given later. 



b. THE CLOSED OR APNEUSTIC TYPE OF RESPIRATORY ORGANS 

That type of respiratory organs in which the spiracles do not 

function is termed 
the closed or 
apneustic* type; it 
exists in naiads and 
in a few aquatic 
lar\'ae. 



I. The Traclieal 
Gills 
In the immature 
insects mentioned 




p;. 137. — Part of a tuft of tracheal gills of a larva of 
Corydalus. 



above, the air m 
the body is purified by means of organs known as tracheal gills. 



*ApneQstic: apneustos {dirvevffTos), without breath 



120 



AN INTRODUCTION TO ENTOMOLOGY 



These are hair-like or more or less plate-like expansions of the body- 
wall, abundantly suppHed with trachege and tracheoles. Figures 136 
and 137 represent a part of a tuft of hair-like tracheal gills of a 
larva of Cory dolus and figure 13S 



a naiad of a 
are separated 



damsel-fly. 
from the air 



In 



these 
the 



a plate-like tracheal gill of 
tracheal gills the tracheoles 
water only by the deHcate 
wall of the tracheal 
gill which admits of 
the transfer of gases 
between the air in the 
tracheoles and the air 
in the water. 

Tracheal gills are 
usually borne by the 
abdomen, sometimes 
by the thorax, and in 
case of one genus of 
stone-flies by the head. 
They pertain almost 
exclusively to the immature stages of insects ; but stone- 
flies of the genus Pteronarcys retain them throughout their 
existence. In the naiads of the Odonata the rectum is 
supplied with many tracheae and functions as a tracheal gill. 





138. — Tracheal gill of a damsel- 
fly: A, entire gill showing the 
tracheae; B, part of gill more 
magnified showing both tracheae (T) 
and tracheoles (t). 



2. Respiration of Parasites 

It is believed that internal parasitic larvse derive their air from air 
that is contained in the blood of their hosts, and that this is done by 
osmosis through the cuticula of the larva, the skin of the larva being 
furnished with a network of fine tracheae (Seurat '99). 



J. The blood-gills 

Certain aquatic larvas possess thin transparent extensions of the 
body wall, which are filled with blood, and serve as respiratory organs. 
These are termed blood-gills. 

Blood-gills have been observed in comparatively few insects; 
among them are certain trichopterous larvae; the larva of an exotic 
beetle, Pelobius; and a few aquatic dipterous larvae, Chironomus and 
Simulium. It is probable that the ventral sacs of the Thysanura, 
described in the account of that order, are also blood-gills. 



THE INTERNAL ANATOMY OF INSECTS 



121 



V. THE CIRCULATORY SYSTEM 

The general features of the circulatory system. — In insects the cir- 
culatory system is not a closed one, the blood flowing in vessels during 
only a part of its course. The greater part of the circulation of this 
fluid takes place in the cavities of the body and of its appendages, 
where it fills the space not occupied by the internal organs. 

Almost the only blood-vessel that exists in insects lies just beneath 
the body-wall, above the alimentary canal (Fig. 105, h). It extends 
from near the caudal end of the abdomen through the thorax into the 
head. That part of it that lies in the abdomen is the heart; the more 
slender portion, which traverses the thorax and extends into the head 
is the aorta. 

On each side of the heart, there is a series 
L %J^ of triangular muscles extending from the heart 

to the lateral wall of the body. These con- 
stitute the dorsal diaphragm or the wings of the 
heart. They are discussed later under the 
head : Suspensoria of the Viscera. 

The heart. — The heart is a tube, which is 
usually closed at its posterior end; at its 
anterior end it is continuous with the aorta. 
The heart is divided by constrictions into 
chambers which are separated by valves (Fig. 
139). The nimiber of these chambers varies 
greatly in different insects; in some, as in 
Phasma and in the larva of Corethra, there is 
only one, in others, as in the cockroach, there 
are as many as thirteen, but usually there are 
not more than eight. The blood is admitted to 
the heart through sKt-like openings, the ostia of 
the heart; usually there is a pair of ostia in the 
lateral walls of each chamber. Each ostitmi is 
furnished with a valve which closes it when the 
chamber contracts. 

The wall of the heart is composed of two dis- 




Fig. 139. — Heart of a 
May -beetle; a, lateral 
aspect of the aorta; b, 
interior of the heart 
showing valves; c, 
ventral aspect of the 
heart and wing-mus- 
cles, the muscles are 



represented as cut away 
from the caudal part of 
the heart; d, dorsal tinct layers: an inner muscular layer ; and an 

outer, connective tissue or peritoneal layer. 

The muscular layer consists chiefly of annular 
muscles; but longitudinal fibers have also been observed. 



aspect of the 
(After Straus-Durck- 
heim). 



122 AN INTRODUCTION TO ENTOMOLOGY 

The pulsations of the heart. — When a heart consists of several 
chambers, they contract one after another, the wave of contraction 
passing from the caudal end of the heart forwards. As the valves 
between the chambers permit the blood to move forward but not 
in the opposite direction, the successive contraction of the chambers 
causes the blood received through the ostia to flow toward the head, into 
the aorta. 

The aorta. — The cephalic prolongation of the heart, the aorta 
(Fig. 139, a), is a simple tube, which extends through the thorax into 
the head, where it opens in the vicinity of the brain. In some cases, 
at least, there are \'alves in the aorta. 

The circulation of the blood. — The circiilation of the blood can be 
observed in certain transparent insects, as in young naiads, in larv£e 
of Trichoptera, and in insects that have just molted. The blood flows 
from the open, cephalic end of the aorta and passes in quite definite 
streams to the various parts of the body-cavity and into the cavities 
of the appendages. These streams, like the ocean currents, have no 
walls but flow in the spaces between the internal organs. After 
bathing these organs, the blood returns to the sides of the heart, 
which it enters through the ostia. 

Accessory circulatory organs. — Accessory pulsating circulatory 
organs have been described in several insects. These are sac-like 
structures which contract independently of the contractions of the 
heart. They have been found in the head in several Orthoptera; in 
the legs of Hemiptera, and in the caudal filaments of Ephemerida. 

VI. THE BLOOD 

The blood of insects is a fluid, which fills the perivisceral cavity, 
bathing all of the internal organs of the body, and flowing out into the 
cavities of the appendages of the body. In only a comparatively 
small portion of its course, is the blood enclosed in definite blood- 
vessels; these, the heart and the aorta are described abo^^e. The 
blood consists of two elements, a fluid plasma and cells similar to th.e 
white corpuscles of the blood of vertebrates, the leucocytes. 

The blood of insects differs greatly in appearance from the blood 
of vertebrates, on account of the absence of red blood-corpuscles. In 
most insects the blood is colorless ; but in many species it has a yellow- 
ish, greenish, or reddish color. In the latter case, however, the color 
is not due to corpuscles of the type which gives the characteristic 
color to the blood of vertebrates. 



THE INTERNAL ANATOMY OF INSECTS 123 

The leucocytes are nucleated, colorless, amoeboid cells similar to 
the white corpuscles of vertebrates, in appearance and function ; they 
take up and destroy foreign bodies and feed upon disintegrating tissue. 
It is believed that the products of digestion of disintegrating tissue by 
the leucocytes pass into the blood and serve to nourish new tissue. 

The blood receives the products of digestion of food, which pass 
in a liquid form, by osmosis, through the walls of the alimentary canal. 
On the other hand it gives up to the tissues which it bathes the 
materials needed for their growth. In insects oxygen is supplied to 
the tissues and gaseous wastes are removed chiefly by the respiratory 
system and not by means of the blood as in vertebrates. 

VII. THE ADIPOSE TISSUE 

On opening the body of an insect, especially of a larva, one of the 
most conspicuous things to be seen is fatty tissue, in large masses. 
These often completely siuround the alimentary canal, and are held 
in place by niimerous branches of the trachese with which they are 
supplied. Other and smaller masses of this tissue adhere to the inner 
surface of the abdominal wall, in the vicinity of the nervous system, 
and at the sides of the body. In adult insects it usually exists in 
much less quantity than in larvae. 

The chief function of the adipose tissue is the storage of nutriment ; 
but it is believed that it also has a urinary function, as concretions of 
uric acid accumulate in it during the life of the insect. 



VIII. THE NERVOUS SYSTEM 

a. THE CENTRAL NERVOUS SYSTEM 

The more obvious parts of the central nerv^ous system are the 
following: a ganglion in the head above the oesophagus, the brain; 
a ganglion in the head below the oesophagus, the subcesophageal 
ganglion; a series of ganglia, lying on the floor of the body cavity in 
the thorax and in the abdomen, the thoracic and the abdominal 
ganglia; two longitudinal cords, the connectives, uniting all of these 
ganglia in a series ; and many nerves radiating from the ganglia to the 
various parts of the body. 

The connectives between the brain and the subcesophageal 
ganglion pass one on each side of the oesophagus ; these are termed the 
crura cerebri, or the legs of the brain; in the remainder of their course, 
the two connectives are quite closely parallel (Fig. 124), 



124 



AN INTRODUCTION TO ENTOMOLOGY 



The series of ganglia is really a double one, there being typically a 
pair of ganglia in each segment of the body ; but each pair of ganglia 
is more or less closely united on the middle line of the body, and 
often appear to be a single ganglion. 

In some cases the ganglia of adjacent segments coalesce, thus 
reducing the nimiber of distinct ganglia in the series. It has been 
demonstrated that the brain is composed of the coalesced ganglia of 
three of the head segments, and the suboesophageal ganglion of the 
coalesced ganglia of the remaining four segments. 




Fig. 140. — Successive stages in the coalescence of thoracic and of abdominal 
gangUa in Diptera; A, Chironomus; B, Empis; C, Tahanus; D, Sar- 
cophaga (From Henneguy after Brandt). 

The three parts of the brain, each of which is composed of the pair 
of ganglia of a head segment, are designated as the protocerebruni, the 
deutocerebrum, and the tritocerebrum, respectively. The protocere- 
brum innervates the compound eyes; the deutocerebrum, the 
antennas; and the tritocerebrum, the labnmi. 

The subcesophageal ganglion is composed of four pairs of primary 
ganglia ; these are the ganglia of the segments of which the mandibles, 
the maxillulae, the maxilla, and the labium, respectively, are the 
appendages. 

The three pairs of thoracic ganglia often coalesce so as to form a 
single ganghonic mass; and usually in adult insects the number of 
abdominal ganglia is reduced in a similar way. 



THE INTERNAL ANATOMY OF INSECTS 



125 



Successive stages in the coalescence of the thoracic and abdominal 
ganglia can be seen by a study of the nervous system of the larva, 
pupa, and adult of the same species, a distinct cephalization of the 
central nervous system taking place during the development of the 
insect. Varying degrees of coalescence of the thoracic and of the 
abdominal ganglia can be seen by a comparative study of the nervous 
systems of different adult insects (Fig. 140). 

The transverse band of fibers that unite the two members of a pair 
of ganglia is termed a commissure. In addition to the commissures 
that pass directly from one member of a pair of ganglia to the other, 

there is in the head a com- 
missure that encircles the 
oesophagus in its passage 
from one side of the brain 
to the other, this is the suh- 
osophageal commissure (Fig. 
141). 

The nerves that extend 




^i-' 



Fig. 141.— Lateral view of the oesophagus of a r ^t^ pptitral chain nf 

caterpillar, showing the suboesophageal com- ^^°^ ^^^ central cnam ot 
missure; b, brain; oe, oesophagus; sc, sub- 
oesophageal commissure; sg, suboesophageal 
ganglion; pg, paired ganglion (After Lienard). 



gangHa to the different 
parts of the body are a part 
of the central nervous sys- 
tem ; the core of each nerve fiber being merely a process of a ganglionic 
cell, however long it ^ 

may be. ^^, ,^ 

b. THE CESOPHAGEAL 



SYMPATHETIC NER- 
VOUS SYSTEM 

In addition to the 
central nervous sys- 
tem as defined above 
there are three other 
nervous complexes 
which are commonly 
described as separate 
systems although 
they are connected 
to the central nervous 
system by nerves. 
These are the oeso- 
phageal sympathetic 




Fig. 142. — Lateral view of the nerves of the head in the 
larva of Corydalus; a, antennal nerve; ao, aorta; ar 
paired nerves connecting the frontal ganglion with the 
brain; h, brain; d, clypeo-labral nerve; con, connective; 
cr, crura cerebri; fg, frontal ganglion; fn, frontal nerve; 
i, unpaired nerve connecting the frontal ganglion with 
the brain; /, labial nerve; Ig, the paired gangHa; md, 
mandibular nerve; m, p, q, s, u, z, nerves of the oesopha- 
geal sympathetic system; mx, maxillary nerve; o, optic 
nerves; oes, oesophagus; ph, pharynx; pn, phar>'ngeal 
nerve; r, recurrent nerve; sc, suboesophageal commis- 
sure; sg, suboesophageal ganglion; st, stomagastric 
nerve; v, ventricular ganglion (From Hammar). 

nervous system, the ventral sympathetic nervous 



126 



AN INTRODUCTION TO ENTOMOLOGY 



system, and the peripheral sensory nervous system. The first of 
these is connected with the brain; the other two, with the thoracic 
and abdominal gangha of the central nervous system. 

The oesophageal sympathetic nervous system is intimately 
associated with the oesophagus and, as just stated, is connected with 
the brain. It is described by different writers under various names; 
among these are visceral, vagus, and stomato gastric. It consists of two, 
more or less distinct, divisions, an unpaired median division and a 
paired lateral division. 

The unpaired division of the oesophageal sympathetic nervous 
system is composed of the following parts, which are represented in 

Figures 141, 143, 143, and 
144: the frontal ganglion 
(Jg), this is a minute gang- 
lion situated above the 
oesophagus a short distance 
in front of the brain; the 
unpaired nerve connecting 
the frontal ganglion with the 
brain (i), this is a small 
nerve extending from the 
brain to the frontal ganglion ; 
the paired nerves connecting 
the frontal ganglion with the 
brain (ar), these are arching 
nerves, one on each side, 
extending from the upper 
ends of the crura cerebri to 
the frontal gangHon; the 
frontal nerve (fn) , this nerve 
arises from the anterior bor- 
der of the frontal ganglion 
and extends cephalad into 
the clypeus, where it bifur- 
cates; the pharyngeal 
nerves (pn), these extend, 
one on each side, from the 
frontal ganglion to the 
lower portions of the pharynx; the recurrent nerve (r), this is a single 
median nerve, which arises from the caudal border of the frontal 
>;anglion, and extends back, passing under the brain and betv»-een the 




Fig. 143. — Dorsal view of the nerves of the 
head in the larva of Corydalus; e, ocelli; 
mnd. mandible; other lettering as in 
Figtire 142 (From Hammar). 



THE INTERNAL ANATOMY OF INSECTS 



127 



aorta and the oesophagus, to terminate in the ventricular ganghon; 
the ventricular ganglion (v), this is a minute ganghon on the middle 
line, a short distance cauda of the brain, and between the aorta and 
the oesophagus; and the stomogastric nerves (st), these are two nerves 
which extend back from the caudal border of the ventricular ganglion, 
they are parallel for a short distance, then they separate and pass, one 
on each side, to the sides of the alimentary canal which they follow 
to the proventriculus. 

The paired division of the oesophageal sympathetic nervous system 
varies greatly in form in different insects. In the larv^a of Corydalus, 
there is a single pair of ganglia (Fig. 142 and 143, Ig), one on each 
side of the oesophagus; each of these ganglia is connected with the 
brain by two nerves {m and u) but they are not connected with each 

other nor with the unpaired division 
of this system. In a cockroach 
(Fig. 144), there are two pairs of 
ganglia {ag and pg); the two ganglia 
of each side are connected with each 
'\ other and with the recurrent nerve of 
the unpaired division. 

As yet comparatively little is 
known regarding the function of the 
oesophageal sympathetic nerv^ous sys- 
tem of insects ; nerves extending from 
it have been traced to the clypeus, 
the muscles of the pharynx, the oeso- 
phagus, the mid-intestine, the salivary 
glands, the aorta, and the heart. 
Its function is probably analogous to 
that of the sympathetic nervous sys- 
tem of Vertebrates. 




Fig. 144. — The oesophageal sympa- 
thetic nervous system of Peri- 
planeta orientalis; the outhnes of 
the brain {b) and the roots of the 
antennal nerve which cover a por- 
tion of the sympathetic nervous 
system are given in dotted lines; 
ag, anterior ganglion; pg, posterior 
ganghon; /g, frontal ganghon; sn, 
nerves of the salivary glands; r, 
recurrent nerve (After Hofer). 



THE VENTRAL SYMPATIlETIC NERV- 
OUS SYSTEM 



The ventral sjonpathetic nervous 
system consists of a series of more or 
less similar elements, each connected 
with a ganglion of the ventral chain 
of the central nervous system. Typi- 
cally there is an element of this system arising in each thoracic and 



128 



AN INTRODUCTION TO ENTOMOLOGY 




abdominal ganglion; and each element consists of a median nerve 
extending from the ganglion of its origin caudad between the two 
connectives, a pair of lateral branches of this median nerve, and one 
or more ganglionic enlargements of each lateral branch. Frequently 
the median nerve extends to the ganglion of the following segment. 
A simple form of this system exists in the larva of 
Cossiis ligniperda (Fig. 122); and a more compli- 
cated one, in Locusia viridissima (Fig. 145). 

Frcm each lateral branch of the median nerve a 
slender twig extends to the closing apparatus of the 
tracheae. 

d. THE PERIPHERAL SENSORY NERVOUS SYSTEM 

Immediately beneath the hypodermal layer of the 
body -wall, there are many bipolar and multipolar 
^,^;^O^rt^1^^\ nerve-cells whose prolongations form a network of 
// \y{\\gs nerves; these constitute the peripheral sensory 
nervous system or the subhypodermal nerve plexus. 

The fine nerves of this system are branches of 
larger nerves which arise in the central nervous sys- 
tem; and the terminal prolongations of the bipolar 

trai sympathetic nerve-cells innervate the sense-hairs of the body- 
nervous sys- ^^n 

tern; g, ganglion . r • r 11 

of the central l^igure 146 represents a surface view 01 a small 
nervous system; p^j.^ q£ ^^le peripheral sensory nervous system of the 
n, nerve; c, con- . t^ 7 ■ r- ttm /> 

nective; m, me- sukworm, Bomoyx men, as figured by Hilton ( 02); 

dian nerve of the ^-^q bases of several sense hairs are also shown. The 
sympathetic sys- 
tem; gs, gang- details of this figure are as follows: h, h, h, the bases 

lion of the sym- ^f sense-hairs; s, s, s, bipolar nerve cells; m, m, m, 

pathetic svstem » > > ; r- 

(From Beriese). multipolar cells; n, n, n, nerves. All of these struc- 
tures are united, forming a net work. Of especial 
interest is the fact that the terminal prolongation of each bipolar 
nerve-cell enters the cavity of a sense-hair and that the other pro- 
longation is a branch of a larger nerve which comes from the central 
nervous system. 

The peripheral sensory nervous system is so delicate that it can 
not be seen except when it is stained by some dye that differentiates 
nervous matter from other tissues. For this purpose the intravitam 
methylen blue method of staining is commonly used. 



Fig. 145. — Part of 
the ventral chain 
of ganglia of Lo- 
custa viridissima 
and of the ven- 



THE INTERNAL ANATOMY OF INSECTS 129 

IX. GENERALIZATIONS REGARDING THE SENSE- 
ORGANS OF INSECTS 

The sense-organs of insects present a great variety of forms, some 
of which are still incompletely understood, in spite of the fact that 
they have been investigated by many careful observers. In the 
limited space that can be devoted to these organs here only the more 
general features of them can be described and some of the disputed 
questions regarding them briefly indicated. 

A classification of the sense-organs. — The different kinds of sense- 
organs are distinguished by the nature of the stimulus that acts on 




Fig. 146. — Surface view of subhypodermal nerves and nerve-cells from 
the silkworm (From Hilton) 

each. This stimulus may be either a mechanical stimulus, a chemicEil 
one, or light. The organs of touch and of hearing respond to mechani- 
cal stimuli; the former, to simple contact with other objects; the 
latter, to vibratory motion caused by waves of sound. The organs of 
taste and of smell are influenced only by soluble substances and it 
seems probable that chemical changes are set up in the sense-cells by 
these substances ; hence these organs are commonly referred to as the 
chemical sense-organs; no criterion has been discovered by which the 
organs of taste and of smell in insects can be distinguished. The 
organs of sight are acted upon by light ; it is possible that the action 
of light in this case is a chemical one, as it is on a photographic plate, 



130 



AN INTRODUCTION TO ENTOMOLOGY 



but the eyes have not been classed among the chemical sense-organs. 
For these reasons the following groups of sense-organs are recognized: 
The mechanical sense-organs. — The organs of touch and of hearing. 
The chemical sense-organs. — The organs of taste and of smell. 
The organs of sight. — The compound eyes and the ocelH. 
The cuticular part of the sense-organs. — In most if not all of the 
sense-organs of insects there exists one or more parts that are of cuti- 
cular formation. The cuticular parts of the organs of sight and of 
hearing are described later, in the accounts of these organs; in this 
place, a few of the modifications of the cuticula found in other sense- 
organs are described. 

Each of the cuticular formations described here is found either 
within or at the outer end of a pore in the cuticula ; as some of these 
formations are obviously setae and others are regarded as modified 
setae, this pore is usually termed the trichopore; it has also been 
termed the neuropore, as it is penetrated by a nerve-ending. 

As the cuticular part of this 
group of sense-organs, those other 
than the organs of hearing and 
of sight, is regarded as a seta, 
more or less modified, these 
organs are often referred to as 
the setiferous sense-organs; they 
are termed the Hautsinnesorgane 
by German writers. 

Special terms have been 
applied to the different types of 
setiferous sense-organs, based on 
the form of the cuticUlar part of 
each; but these types cannot 
be sharply differentiated as 
intergrades exist between them. 
In Figure 147 are represented 
the cuticular parts of several of 
these different types; these are 
designated as follows : 

The thick-walled sense-hair, 
sensillum trichodeum. — In this 
type the cuticular part is a seta, 
the base of which is in an alveolus at the end of a trichopore and is 
connected with the wall of the trichopore by a thin articular mem- 
brane (Fig. 147, a.) 




Fig. 147. — Various forms of the cuticular 
portion of the setiferous sense-organs. 
The lettering is explained in the text. 



THE INTERNAL ANATOMY OF INSECTS 131 

If the sense-hair is short and stout, it is termed by some writers 
a sense-bristle, sensilhtm chceticum; but there is little use for this dis- 
tinction. 

In the thick-walled sense-hairs, the wall of the seta is fitted to 
receive only mechanical stimuli, being relatively thick, and as these 
organs lack the characteristic features of the organs of hearing, they 
are believed to be organs of touch. 

The sense-cones - — -The sense-cones vary greatly in form and in their 
relation xo the cuticula of the body- wall ; their distinctive feature is 
that they are thin-walled. For this reason, they are believed to be 
chemical sense-organs, the thinness of the wall of the cone permitting 
osmosis to take place through it. In the sense-cones, too, there is no 
joint at the base, as in the sense-hairs, the articular membrane being 
of the same thickness as the wall of the cone ; there is, therefore, no 
provision for movement in response to mechanical stimuli. 

In one type of sense-cone, the sensillum basiconicum, the base of 
the cone is at the surface of the body- wall (Fig. 147, 6). In another 
type, sensillum caloconicum, the cone is in a pit in the cuticula of the 
body-wall (Fig. 147, c). Two forms of this type are represented in 
the figure; in one, the sense-cone is conical; in the other, it is fungi- 
form. Intergrades between the basiconicum and the coeloconictmi 
types exist (Fig. 147, d). 

The flask-like sense-organ, sensillum ampullaceum. — This is a 
modification of the sense-cone type, the characteristic featiu^e of 
which is that the cone is at the bottom of an invagination of the articu- 
lar membrane; in some cases the invagination is very deep so that 
the cone is far within tlie body- wall (Fig. 147, ^) ; intergrades between 
this fonn and the more common sensillum coeloconicum exist (Fig. 

147, /). 

The pore-plate, sensillum placodeum. — In this type the cuticular 
part of the organ is a plate closing the opening of the trichopore ; in 
some cases, this plate is of considerable thickness with a thin articular 
membrane (Fig. 147, g); in others it is thin throughout (Fig. 147, h). 

The olfactory pores. — This type of sense-organ is described later. 

X. THE ORGANS OF TOUCH 

The organs of touc. . are the simplest of the organs of special sense 
of insects. They are widely distributed over the surface of the body 
and cf its appendages. Fach consists of a seta, with all the character- 
istics of setae already ar^scnoed, a tricho|,en cell, which excreted the 



132 AN INTRODUCTION TO ENTOMOLOGY 

seta, and a bipolar nerv^e-cell. These organs are of the type known as 
sensillum trichodeum referred to in the preceding section of this 
chapter. 

According to the observations of Hilton (02) the terminal pro- 
longation of the nerve-cell enters the hair and ends on one side of it at 
some distance from its base (Fig. 148). The proximal part of this 
nerve-cell is connected with the peripheral sensory nervous system, as 
already described (page 128). 

The presence of this nervous connection is believed to distinguish 
tactile hairs from those termed clothing hairs, and from the scales 
that are modified setee. If this distinction is a good one, it is quite 
probable that many hairs and scales that are now regarded as merely 
clothing will be found to be sense-organs, when studied by improved 
histological methods. In fact Guenther (01) and others have shown 
that some of the scales on the wings of Lepidoptera, especially those 
on the veins of the wings, are supplied with nerves ; but the function 
of these scales is unknown. 

Hilton states that he "found no evidence to indicate nerves ending 
in gland cells or trichogen cells by such branches as have been described 
and figured by Blanc ('90), but in every case the very fine nerve 
termination could be traced up past the hypodermal cell la^-er with 
no branches." Many figures of unbranched nerve fibers ending in 
sense-hairs are also given by O. vom Rath ('96). 

A very different form of nerve-endings in sense-hairs is given by 
Berlese ('09, a). This author represents the nerv^e extending to a 
sense-hair as dividing into many bipolar nen^e-endings. 



XL THE ORGANS OF TASTE AND OF SMELL 
{The chemical sense-organs) 

It is necessary to discuss together the organs of taste and of smell, 
as no morphological distinction between them has been discovered. 
If a chemical sense-organ is so located that it comes in contact with 
the food of the insect, it is commonly regarded as an organ of taste, if 
not so situated, it is thought to be an organ of smell. In the present 
state of our knowledge, this is the only distinction that can be made 
between these two kinds of organs. 

Many experiments have been made to determine the function of 
the various chemical sense-organs but the results are, as yet, far from 
conclusive. The problem is made difficult by the fact that these 



THE INTERNAL ANATOMY OF INSECTS 



133 



organs are widely distributed over the body and its appendages, and 
in some parts, as on the antenna of many insects, several different 
types of sense-organs are closely associated. 

Those organs that are characterized by the presence of a thin- 
walled sense-cone (Fig. 147, h-f) or by a pore-plate (Fig. 147, g, h) are 
believed to be chemical sense-organs. It is maintained by Berlese 
('09, a) that an essential feature of these chemical sense-organs is the 
presence of a gland -cell, the excretion ofwhich, passing through the thin 
wall of the cuticular part, keeps the outer surface of this part, the 
sense-cone or pore-plate, moist and thus fitted for the reception of 
chemical stimuli. According to this view a chemical sense-organ 
consists of a cuticular part, a trichogen cell or cells which produced 




Fig. 148. — Sections through the body-wall and sense-hairs of the silk- 
worm; c, cuticula; h, hair; hy, hypodermis; n, nerve; 5, bipolar 
nerve-cell (From Hilton). The line at the right of the figure indi- 
cates one tenth miUimeter. 



this part, a gland-cell which excretes a fluid which keeps the part 
moist, and a nerve-ending. 

It is interesting to note that tactile hairs may be regarded as 
specialized clothing hairs, specialized by the addition of a nervous 
connection, and that sense-cones and pore-plates may be regarded as 
specialized glandular hairs with a nervous connection; in the latter 
case, the specialization involves a thinning of the wall of the hair so as 
to permit of osmosis through it. 

In the diiTerent accounts of chemical sense-organs there are 
marked differences as regards the form of the nerve-endings. In 
many of the descriptions and figures of these organs the nerv^e-ending 
is represented as extending unbranched to the chitinous part of the 
organ, resembling in this respect those represented in Figure 148. 
In other accounts the gland-cell is surrounded by an involucre of 
nerve-cells (Fig. 149). 



13-t 



AN INTRODUCTION TO ENTOMOLOGY 



In the types of chemical sense-organs described above the action 
of the chemical stimuli is supposed to be dependent upon osmosis 

through a delicate 
cuticular membrane. 
It should be noted, 
however, that sev- 
eral writers have de- 
scribed sense-cones in 
which there is a pore ; 
but the accuracy of 
these observations is 
doubted by other 
writers. 

A very different 
type of sense-organs 
which has been termed 
olfactory pores is de- 
scribed in the conclud- 
ing section of this 
chapter. 




Fig. 149.— Section of the external layers of the wall of 
an antenna of A crida turrita; Ct, cuticula; Ip, hypo- 
dermis; N, nerve; Nv, involucre of nerve-cells sur- 
rounding the glandular part of a sense-organ; Sbc, 
sensillum basiconicum; Sec, sensillum coeloconicum. 
Three sense-organs are figured; a surface view of the 
first is represented, the other two are shown in sec- 
tion. (From Berlese). 



XII. THE ORGANS OF SIGHT 



a. THE GENERAL FEATURES 

The two types of eyes of insects. — It is shown in the preceding 
chapter that insects possess two types of eyes, the ocelli or simple eyes 
and the compound or facetted eyes. 

Typically both types of eyes are present in the same insect, but 
either may be wanting. Thus many adult insects lack ocelli, while 
the larvae of insects with a complete metamorphosis lack compound 
eyes. 

When all are present there are two compound eyes and, typically 
two pairs of ocelli ; but almost invariably the members of one pair of 
ocelli are united and form a single median ocellus. The median ocel- 
lus is wanting in many insects that possess the other two ocelli. 

The distinction between ocelli and compound eyes. — The most 
obvious distinction between ocelli and compound eyes is the fact that 
in an ocellus there is a single cornea while in a compound eye there are 
many. Other features of compound eyes have been regarded as dis- 
tinctively characteristic of them; but in the case of each of these 
features it is found that they exist in some ocelli. 



THE INTERNAL ANATOMY OF INSECTS 135 

Each ommatidium of a compound eye has been considered as a 
separate eye because its nerve-endings constituting the retinula are 
isolated from the retinulse of other ommatidia by surrounding acces- 
sory pigment cells; but a similar isolation of retinulas exist in some 
ocelli. 

It has also been held that in compound eyes there is a layer of cells 
between the corneal hypodermis and the retina, the crystalline-cone- 
cells, which is absent in ocelli ; but in the ocelli of adult Ephemerida 
there is a layer of cells between the lens and the retina, which, at least, 
is in a position analogous to that of the crystalline-cone-cells; the 
two may have had a different origin, but regarding this, we have, as 
yet, no conclusive data. 

The absence of compound eyes in most of the Apterygota. — 

Typically insects possess both ocelli and compound eyes ; when either 
kind of eyes is wanting it is evidently due to a loss of these organs and 
not to a generalized condition. Although compound eyes are almost 
universally absent in the Apterygota in the few cases where they 
are present in this group they are of a highly developed type and not 
rudimentary; the compound eyes of Machilis, for example, are as 
perfect as those of winged insects. 

The absence of compound eyes in larvae. — The absence of com- 
pound eyes in larvse is evidently a secondary adaptation to ilieir 
particular mode of life, like the internal development of wings in the 
same forms. In the case of the compound eyes of larvae, the develop- 
ment of the organs is retarded, taking place in the pupal stage instead 
of in an embryonic stage, as is the case with nymphs and naiads. 

While the development of the compound eyes as a whole is retarded 
in larvffi, a few ommatidia may be developed and function as ocelli 
during larval life. 

h. THE OCELLI 

There are two classes of ocelli found in insects : first, the ocelli of 
adult insects and of nymphs and naiads, which may be termed the 
primary ocelli; and second, the ocelli of most larvag possessing ocelli, 
which may be termed adaptive ocelli. 

The primary ocelli. — The ocelli of adult insects and of nymphs and 
naiads having been orig'nally developed as ocelli are termed the 
primary ocelli. Of these there are typically two pairs; but usually 
when they are present there are only three of them, and in many cases 
only a single pair. 



136 



AN INTRODUCTION TO ENTOMOLOGY 



When there are three ocelH, the double nature of the median ocel- 
lus is shown by the fact that the root of the nerve is double, while that 
of each of the other two is single. 

In certain generalized insects, as some Plecoptera, (Fig. 150) all of 
the ocelli are situated in the front; but in most insects, the paired 
ocelli have either migrated into the suture between the front and the 
vertex (Fig. 151), or have proceeded farther and are situated in the 
vertex. 

The structure of primary ocelli is described later. 
The adaptive ocelli. — Some larvae, as those of the Tenthredinidae, 
possess a single pair of ocelli, which in their position and in their 
structure agree with the ocelli of the adult insects ; these are doubtless 
primary ocelli. But most larvae have lost the primary ocelli; and 
if they possess ocelli the position of them and their structure differ 
greatly from the positions and structure of primary ocelli. 

Except in the few cases where primary ocelli 
have been retained by larvae, the ocelli of 
larvae are situated in a position corresponding 
to the position of the compound eyes of the 
adult (Fig. 152); and there are frequently 
several of these ocelli on each side of the head. 
This has led to the belief that they represent 
a few degenerate ommatidia, which have been 
retained by the larva, while the development of 
the greater nimiber of ommatidia has been 
retarded. For this reason they are termed 




Fig. 150. — Head of 



naiad of Pteronacys; 
dt, spots in the cnti- 
cula beneath which 
the dorsal arms of the adaptive ocelli. 

tached; the three The number of adaptive ocelli varies greatly, 

oceUi are on the front and sometimes is not con- 

(F), between these , , . . ,, 

two spots. stant m a species; thus 

in the larva of Corydalus, 
there may be either six or seven ocelli on each 
side of the head. 

There are also great variations in the struct- 
ure of adaptive ocelli. These variations pro- 
bably represent different degrees of degeneration 
or of retardation of development. The extreme 
of simplicity is found in certain dipterous lar\^as ; 
according to Hesse ('01) an ocellus of Cerato- 
pogon consists of only two sense-cells. As examples of com- 
plicated adaptive ocelli, those of lepidopterous larv^ae can be cited. 




Fig. 151. — Head of 
cricket. 



THE INTERNAL ANATOMY OF INSECTS 



137 




Fig. 152. — Head of a 
larva of Corydalus, 
dorsal aspect. 



The ocellus cf Gastropacha rubi, which is described and figured by 

Pankrath ('90), resembles in structure, to a remarkable degree, an 
ommatidium, and the same is true of the ocellus 
of the lar\^a of Arctia caja figured by Hesse (01). 
The structure of a visual cell. — The dis- 
tinctively characteristic feature of eyes is the 
presence of what is termed visual cells. In 
insects, and in other arthropods, a visual cell 
is a nerve-end-cell, which contains a nucleus 
and a greater or less amount of pigment, 
and bears a characteristic border, termed the 
rhabdomere; this is so called because it forms 
a part of a rhab- 
dom. 

The visual 

cells are grouped in such a way that the 

rhabdomeres of two or more of them 

are united to form what is known as a 

rhabdcm or optic rod. A group of two 

visual cells with therhabdom formed by 

their united rhabdomeres is shown in 

Figure 153, AandB. 

The form of the rhabdomere varies 

greatly in the visual cells of different 

insect eyes; and the number of rhab- 
domeres that enter into the composi- 
tion of a rhabdom also varies. 

Figure 153, C represents in a dia- 
grammatic manner the structure of 

rhabdomere as described by Hesse ('01). 

The rhabdomere (r) consists of many 

minute rodleti each with a minute knob 

at its base and connected with a nerve 

fibril. 

The structure cf a primary ocellus. 

— The primary ocelli vary greatly in 

the details of the form of their parts, 

but the essential features of their structure are illustrated by the 

accompanying diagram (Fig. 154). 

In some ocelli, as for example the lateral ocelli of scorpions, 

the visual cells are interpolated among ordinary hypodermal cells. 




Fig. 153. — Two visual cells from 
an ocellus of a pupa of Apis 
mellifica. A, longitudinal sec- 
tion ; B, transverse section; n, 
n, nerves; iiu, nucleus; r, 
rhabdom; p, pigment (After 
Redikorzew), C, diagram il- 
lustrating the structure of a 
rhabdomere; r, rhabdomere; 
c, cell-body (From Berlese after 
Hesse). 



138 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. 154. — A diagram illustrating the structtire of 
a primary ocellus; c, cornea; c. hy, corneal 
hypodermis; ret, retina; n, ocellar nerve; p, 
accessory pigment cell; r, rhabdom. 



the two kinds forming a single layer of cells beneath the 
cornea; but in the ocelli of insects, the sense-cells form a distinct 

layer beneath the hypo- 
dermal cells. In this 
type of ocellus the fol- 
lowing parts can be dis- 
tinguished : 

The cornea. — T h e 
cornea (Fig. 154, c) is a 
transparent portion of 
the cuticula of the body- 
wall ; this may be lenti- 
cular in form or not. 

Tlie corneal hypoder- 
mis. — The hypodermis 
of the body-wall is con- 
tinued beneath the 
cornea (Fig. 154, c. hy.) ; 
this part of the hypo- 
dermis is termed by 
many writers the vitrecus 
layer of the ocellus; but the term corneal hypodermis, being a self- 
explanatory term, is preferable. Other terms have been applied to it, 
as the lentigen layer and the corneagen, both referring to the fact that 
this part of the hypodermis produces the cornea. 

The retina. — Beneath the corneal hypodermis is a second cellular 
layer, which is termed the retina, being composed chiefly or entirely of 
visual cells (Fig. 154, ret). 

The visual cells of the retina are grouped, as described above (Fig. 
153), so that the rhabdomeres of several of them, two, three or four, 
unite to form a rhabdom; such a group of retinal cells is termed a 
retinula. 

The visual cells are nerve-end-cells, each constituting the termina- 
tion of a fiber of the ocellar nerve, and are thus connected with the 
central nervous system. 

Accessory pigment cells. — In some ocelli there are densely pig- 
mented cells between the retinulas, which serve to isolate them in a 
similar way to that in which the retinula of an ommatidium of a com- 
pound eye is isolated (Fig. 154, p). Even in cases where accessory 
pigment cells are wanting a degree of isolation of the rhabdoms of the 
retinulse of an ocellus is secured by pigment within the visual cells 
(Fig. 153, P)- 



THE INTERNAL ANATOMY OF INSECTS 



139 



Ocelli of Ephemerida. — It has been found that the ocelli of certain 
adult Ephemerida differ remarkably from the more com-mon type of 
ocelli described above. These peculiar ocelli have been described and 
figured by Hesse ('oi) and Seiler ('05). In them the cuticula over the 
ocellus, the comea, is arched but not thickened and the corneal hypo- 
dermis is a thin layer of cells immediately beneath it. Under the 
hypodermis there is a lens-shaped mass of large polygonal cells; and 
between this lens and the retina there is a layer of closely crowded 
columnar cells. 

The development of these ocelli has not been studied; hence the 
origin of the lens-shaped mass of cells and of the layer of cells between 
it and the retina is not known. 

C. THE COMPOUND EYES 

A compound eye consists of many 
quite distinct elements, the ommatidia, 
each represented externally by one of 
the many facets of which the cuticular 
layer of the eye is composed. As the 
ommatidia of a given eye are similar, 
a description of the structure of one 
will serve to illustrate the structure of 
the eye as a whole. 

The structure of an ommatidium. — 
The compound eyes of different insects 
vary in the details of their structure; 
but these variations are merely modi- 
fications of a common plan ; this plan is 
well -illustrated by the compound eyes 
of Machilis, the structure of which was 
worked out by Seaton ('03). Figure 
155 represents a longitudinal section 
and a seiies of transverse sections of an 
ommatidium in an eye of this insect, 
which consists of the following parts. 
Ml , The cornea. — The cornea is a hexa- 

inr-» gonal portion of the cuticular layer of 

the eye and is biconvex in form (Fig. 
155, c). 

The corneal hypodermis. — Beneath 
each facet of the cuticular layer of the eye are twe hypodermal cells 




Fig- 155- — An ommatidium of 
Machilis. The lettering is ex- 
plained in the text. 



140 AN INTRODUCTION TO ENTOMOLOGY 

which constitute the corneal hypodermis of the ommatidium. These 
cells are quite distinct in Machilis and their nuclei are prominent 
(Fig. 155, hy); but in many insects they are greatly reduced, and 
consequently are not represented in many of the published figures 
of compound eyes. 

The crystalline-cone-ceUs. — Next to the corneal hypodermis there 
are four cells, which in one type of compound eyes, the eucone eyes, 
form a body known as the crystalline-cone, for this reason these 
cells are termed the crystalline-conc-cells (Fig. 155, cc). Two of 
these cells are represented in the figure of a longitudinal section 
and all four, in that of a transverse section. In each cell there is a 
prominent nucleus at its distal end. 

The iris -pigment-cells. — Surrounding the crystalline-cone-cells and 
the corneal hypodermis, there is a curtain of densely pigmented cells, 
which serves to exclude from the cone light entering other ommatidia; 
for this reason these cells are termed the iris -pigment (Fig. 155, i). 
They are also known as the distal retinula cells; but as they are not a 
part of the retina this term is misleading. 

There are six iris -pigment -cells surrounding each crystalline -cone; 
but as each of these cells forms a part of the iris of three adjacent 
ommatidia, there are only twice as many of these cells as there are 
ommatidia. This is indicated in the diagram of a transverse section 
(Fig. 15s, ^). 

The retinula. — At the base of each ommatidium, there is a group 
of visual cells forming a retinula (Fig. 1 55, r) ; of these there are seven 
in Machilis; but they vary in number in the eyes of different insects. 
The visual cells are so grouped that their united rhabdomeres form a 
rhabdom, which extends along the longitudinal axis of the ommati- 
dium (Fig. 155, r/j). The distal end of the rhabdom abuts against the 
proximal end of the crystalline-cone ; and the nerve-fibers of which the 
visual cells are the endings pass through the basement membrane 
(Fig. 155, b) to the optic nerve. 

The visual cells are pigmented and thus aid in the isolation of the 
ommatidium. 

The accessory pigment -cells. — In addition to the two kinds of pig- 
ment-cells described above there is a variable niunber of accessory 
pigment -cells (Fig. 155, ap), which lie outside of and overlap them. 

From the above it will be seen that each ommatidium of a eucone 
eye is composed of five kinds of cells, three of which, the corneal hypo- 
dermis, the crystalline-cone-cells, and the retinular cells produce solid 
structures; and three of them are pigmented. 



THE INTERNAL ANATOMY OF INSECTS 141 

Three types of compound eyes are recognized: first, the eucone 
eyes, in these each ommatidium contains a true cry staUine -cone, as 
described above, and the nuclei of the cone-cells are in front of the 
cone; second, the pseudocone eyes, in these the four cone-cells are 
filled with a transparent fluid medium, and the nuclei of these cells are 
behind the refracting body; and third, the acone eyes, in which 
although the four cone -cells are present they do not form a cone, either 
solid or liquid. 

d. THE PHYSIOLOGY OF COMPOUND EYES 

The compound eyes of insects and of Crustacea are the most com- 
plicated organs of vision known to us. It is not strange therefore, that 
the manner in which they function has been the subject of much dis- 
cussion. It is now, however, comparatively well-understood; 
although much remains to be determined. 

In studying the physiology of compound eyes, three sets of struc- 
tures, found in each ommatidium, are to be considered: first, the 
dioptric apparatus, consisting of the cornea and the crystalline -cone; 
second, the percipient portion, the retinula, and especially the rhab- 
dom; and third, the envelope of pigment, which is found in three 
sets of cells, the iris pigment -cells, the retinular cells, and the accessory 
or secondary pigment- cells. 

The dioptrics of compound eyes is an exceedingly complicated 
subject ; a discussion of it would require too much space to be intro- 
duced here. It has been quite fully treated by Exner ('91). to whose 
work those especially interested in this subject are referred. The 
im.portant point for our present discussion is that by means of the 
cornea and the crystalline-cone, light entering the cornea from within 
the limits of a certain angle passes through the cornea and the crystal- 
line-cone to the rhabdom, which is formed of the combined rhab- 
domeres of the nerve-end-cells, constituting the retinula, the precipient 
portion of the ommatidium. 

The theory of mosaic vision. — The first two questions suggested by 
a study of physiology of compound eyes have reference to the nature 
of the vision of such an eye. What kind of an image is thrown upon 
the retinula of each ommatidium? And how are these images com- 
bined to form the image perceived by the insect? Does an insect 
with a thousand ommatidia perceive a thousand images of the object 
viewed or only one? 

The theory of mosaic vision gives the answers to these questions. 
This theory was proposed by J. Muller in 1826; and the most recent 



142 



j^N INTRODUCTION TO ENTOMOLOGY 



investigations confirm it. The essential features of it are the follow- 
ing: only the rays of light that pass through the cornea and the 
crystalline -cones reach the precipient portion of the eye, the others fall 
on the pigment of the eye and are absorbed by it ; in each ommatidium 
the cornea transmits to the crystalline -cone light from a very limited 
field of vision, and when this light reaches the apex of the crystalline- 
cone it forms a point of light, not an image; hence the image formed 
upon the combined retinute is a mosaic of points of light, which com- 
bined make a single image, and this rmage is an erect one. 

Figure 156 will serve to illustrate the mosaic theory of vision. 
In this figi-ire are represented the corneas (c), the crystalline -cones 
(cc), and the rhabdoms (r.) of several adja- 
cent ommatidia. It can be seen, from this 
diagram, that each rhabdom receives a 
point of light which comes from a limited 
portion of the object viewed (O) ; and that 
the image (I) received by the percipient 
portion of the eye is a single erect image, 
formed by points of light, each of which 
corresponds in density and color to the 
corresponding part of the object viewed. 
The distinctness of vision of a com- 
pound eye depends in part upon the num- 
ber and size of the ommatidia. It ca n be 
readily seen that the image formed by 
many small ommatidia will represent the 
details of the object better than one formed 
by a smaller number of larger ommatidia ; the smaller the portion of 
the object viewed by each ommatidium the more detailed -will be the 
image. 

The distinctness of the vision of a compound eye depends also on 
the degree of isolation of the light received by each ommatidium, 
which is determined by the amount and distribution of the pigment. 
Two types of compound eyes, differing in the degree of isolation of the 
light received by each ommatidiiun, are recognized; to one type has 
been applied the term day-eyes, and to the other, night-eyes. 

Day-eyes. — The type of eyes known as day-eyes are so-called 
because they are fitted for use in the day-time, when there is an 
abundance of light. In these eyes the envelope of pigment sur- 
rounding the transparent parts of each ommatidiimi is so complete 
that only the light that has traversed the cornea and crystalline-cone 




Fig. 156. — Diagram illustrat- 
ing the theory of mosaic 
vision. 



THE INTERNAL ANATOMY OF INSECTS 



143 



of that ommatidimn reaches its rhabdom. The image fonned in 
such an eye is termed by Exner an apposed image; because it is former^ 
by apposed points of Hght, falHng side by side and not overlapping. 
Such an image is a distinct one. 

Night-eyes. — In the night-eyes the envelope of pigment surround- 
ing the transparent parts of each ommatidiimi is incomplete ; so that 
rays of light entering several adjacent corneas can reach the same 
retinula. In such an eye there will be an overlapping of the points of 
light; the image thus formed is termed by Exner a superimposed 
image. It is obvious that such an image is not as distinct as an ap- 
posed image. It is also obvious that a limited amount of light will 
produce a greater impression in this type of eye than in one where a 
considerable part of the light is absorbed by pigment. Night-eyes are 
fitted to perceive objects and the movement of objects in a dim light, 
but only the more general features of the object can be perceived by 
them. 

Eyes with double function. — It is a remarkable fact that with 
many insects and Crustacea the compound eyes function in a bright 
^ p light as day-eyes and in a dim light as night- 

eyes. This is brought about by movements in 
the pigment. If an insect having eyes of this 
kind be kept in a light place for a time and then 
killed while still in the light, its eyes will be found 
to be day-eyes, that is eyes fitted to form apposed 
images. But if another insect of the same 
species be kept in a dark place for a time and 
then killed while still in the dark, its eyes will be 
found to be night-eyes, that is eyes fitted to 
form superimposed images. 

Figure 157 represents two preparations 
showing the structure of the compound eyes of 
a diving-beetle, studied by Exner. In one 
(Fig. 157, A), each rhabdom is surrounded by an 
envelope of pigment, so that it can receive only 
the light passing through the crystalline-cone of 
the ommatidium of which this rhabdom is a part. 
This is the condition found in the individual 
killed in the light, and illustrates well the struct- 
ure of a day-eye. In the other preparation (Fig. 
157, i5), which is from an individual killed in the dark, it can be seen 
that the pigment has moved up between the crystalline -cones so that 




Fig. 157. — Ommatidia 
from eyes of Colym- 
betes; A, day-eye 
condition; B, night- 
eye condition (From 
Exner). 



144 AN INTRODUCTION TO ENTOMOLOGY 

the light passing from the tip of a cone may reach several rhabdoms, 
making the eye a night-eye. These changes in the position of the 
pigment are probably due to amoeboid movements of the cells. 

Divided Eyes. — In many insects each compound eye is divided 
into two parts; one of which is a day-eye, and the other a night-eye. 
The two parts of such an eye can be readily distinguished by a differ- 
ence in the size of the facets ; the portion of the eye that functions 
as a day-eye being composed of much smaller facets than that which 
functions as a night-eye. 

A study of the internal structure of a divided eye shows that the 
distribution of the pigment in the part composed of smaller facets is 
that characteristic of day-eyes ; while the part of the eye composed of 
larger facets is fitted to produce a superimposed image, which is the 
distinctive characteristic of night-eyes. 

Great differences exist in the extent to which the two parts of a 
divided eye are separated. In many dragon-flies the facets of a part 
of each compound eye are small, while those of the remainder of the 
eye are much larger ; but the two fields are not sharply separated. In 
some Blepharocera the two fields are separated by a narrow band in 
which there are no facets, and the difference in the size of the facets of 
the two areas is very marked. The extreme condition is reached in 

certain May-flies, where the two 
parts of the eye are so widely separa- 
ted that the insect appears to have 
two pairs of compound eyes (Fig 158). 
The tapetum. — In the eyes of 
many ariimals there is a structure 
that reflects back the light that has 
entered the eye, causing the well- 
known shining of the eyes in the 
dark. This is often observed in the 
Fig. i58.-Front of head of Cloeon, ^f ^^^g ^^^ ^^ ^^le eyes of moths 

showing divided eyes; a, night-eye; ; , i- 1 

i, day-eye; c, ocellus (From Sharp), that are attracted to our light at 

night. The part of the eye that 
causes this reflection is termed a tapetum. The supposed function of a 
tapetimi is to increase the effect of a faint light, the light being caused 
to pass through the retina a second time, when it is reflected from the 
tapetimi. 

The structure of the tapetum varies greatly in different animals; 
in the cat and other carnivores it is a thick layer of wavy fibrous tissue; 
in spiders it consists of a layer of cells behind the retina containing 




THE INTERNAL ANATOMY OF INSECTS 



145 



small crystals that reflect the light ; and in insects it is a mass of fine 
tracheae surrounding the retinula of each ommatidium. 



XIII. THE ORGANS OF HEARING 




Fig. 159. — Side view of a locust with the wings 
removed; t, tympanum. 



a. THE GENERAL FEATURES 

The fact that in many insects there are highly specialized organs 
for the production of sounds indicates that insects possess also organs 
of hearing; but in only a few cases are these organs of such form 

that they have been gen- 
erally recognized as ears. 
The tympana. — In 
most of the jimiping 
Orthoptera there are 
thinned portions of the 
cuticula, which are of a 
structure fitted to be put 
in vibration by waves of 
sound. For this reason these have been commonly regarded as organs 
of hearing, and have been termed tympana. In the Acridiidae, there 
is a tympanum on each side of the first abdominal segment (Fig. 
159); and in the Locustidee and in the Gryllidas, there is a pair of 
tympana near the proximal 
end of each tibia of the first 
pair of legs (Fig. 160). 

The chordotonal organs. — 
An ear to be effective must 
consist of something more than 
a membrane that will be put 
in vibration by means of 
sound; the vibrations of such 
a tympantmi must be trans- 
ferred in some way to a nerv- 
vous structure that will be 
influenced by them if the 
sound is to be perceived. Such 
structures, closely associated 

with the tympana of Orthoptera, were discovered more than a half 
century ago by Von Siebold (1844) and have been studied since by 
many investigators . The morphological unit of these essential auditory 




Fig. 160. — Fore leg of a katydid; /, tympa- 
num. 



146 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. i6i. — Diagrammatic representation of the 
auditory organs of a locustid (After Graber). 



structures of insects is a more or less peg-like rod contained in a tubular 
nerve-ending (Fig. i6i, A and B); this nerve-ending may or may 

not be associated with a 
specialized t5rmpanum. 
To all sense-organs char- 
acterized by the presence 
of these auditory pegs, 
Graber ('82) applied the 
term chordotonal organs or 
fiddle-string-like organs. 
The scolopale and 
the scolopophore. — The 
peg-like rod 
characteris- 
tic of a chor- 
dotonal organ of an insect was named by Graber the 
scolopale; and to the tubular nerve-ending containing 
the scolopale, he applied the term scolopophore. 

The integumental and the subintegumental scolopo- 
phores. — ^With respect to their position there are two 
types of scolopophores ; in one, the nerve-ending is 
attached to the body-wall (Fig. 161, A); in the other, it 
ends free in the body-cavity (Fig. 161, B). These two 
types are designated respectively as integumental scolo- 
pophores and subintegumental scolopophores. 

The structure of a scolopophore. — In a scolopophore 
there can be distinguished an outer sheath (Fig. 161, I), 
which appears to be continuous either with the basement 
membrane of the hypodermis or with that of the 
epitheliirm of a trachea, and within this sheath the 
complicated nerve-ending; this nerve-ending is repre- 
sented diagrammatically in Figure 161 from Graber and in 
detail in Figure 162 from Hess ('17). 

In Figure 162 the following parts are represented: a 
bipolar sense-cell {sc) with its nucleus (sen) ; the proximal 
pole of this sense -cell is connected with the central nerv- 
ous system by a nerve; and its distal pole is connected phoreof the 
with the scolopale {s) by an axis -fiber (a/); surrounding mental type 
the distal prolongation of the sense-cell and the scolopale (From 
there is an enveloping or accessory cell {ec), in which ^^^s). 
there is a prominent nucleus {ecu) ; distad of the enveloping cell is 



THE INTERNAL ANA.TOMY OF INSECTS 147 

the cap-cell {c:), in which there is a nucleus {ecu); extending from 
the end -knob (ek) of the scolopale and surrounded by the cap -cell 
there is an attacliment fiber or terminal ligament {tl) , by which the 
scolopophore is attached to the body-wall, the scolopophore repre- 
sented being of the integumental type; at the base of the scolopale 
and partly surrounding it, there is a vacuole (v) . 

The structure of a scolopale. — The scolopalas or auditory pegs are 
exceedingly minute and are quite uniform in size, regardless of the size 
of the insect in which they are ; but they vary in form in different 
insects. They are hollow (Fig. 162,5); but the wall of the scolopale 
is almost always thickened at its distal end, this forming an end-knob 
(Fig. 162, ^^). They are traversed by the axis -fiber of the sense -cell. 
The vacuole at the base of the scolopale connects with the limien of 
the scolopale; this vacuole is filled with watery 
fluid. 

In Figure 163 is shown a part of the scolopo- 
phore represented in Figure 162, more enlarged 
@(A), and three cross-sections (B, C, D) of the 
'■ scolopale. The wall of the scolopale is composed 
at either end of seven ribs (r), each of which is 
-(.^ij.;- divided in the central portion, making fourteen 
^--— ^ ribs in this part. The entire scolopale, except 
possibly the terminal ligament, is bathed in the 
watery liquid, and is free to vibrate (Hess '17). 

Fig. i63.-Part of the j^ g^o^ld be remembered that the scolopate of 
scolopophore shown . . . 

in Figure 162 more different insects vary greatly in form; the one 
enlarged (From figu^j-ed here is merely given as an example of 
one type. 

The simpler forms of chordotonal organs. — In the simplest form 
of a chordotonal organ there is a single scolopophore; usually, how- 
ever, there are two or more closely parallel scolopophores. In figure 
164, which represents a chordotonal organ found in the next to the 
last segment of the body of a larv^a of ChironomMS, these two types are 
represented, one part of the organ being composed of a single scolopo- 
phore, the other of several. 

The chordotonal ligament. — In Figure 164 the nerve connecting 
the chordotonal organ with the central nervous system is represented 
at n; and at U is shown a structure not yet mentioned, the chordo- 
tonal ligament, which is found in many chordotonal organs. Figure 
165 is a diagrammatic representation of the relations of the chordo- 
tonal organs of a larva of Chironomus to the central nen.^ous system 



148 



AN INTRODUCTION TO ENTOMOLOGY 



and to the body-wall. Here each chordotonal organ is approxi- 
mately T-shaped; the proximal nerve forming the body of the T; 

the scolopophore, one 

arm; and the chor- 
dotonal ligament, the 

other arm. 

It will be observed 

that in this type of 

chordotonal organ 

the scolopophore and 

the ligament form a 

fiddle-string-like 

structure between two 

points in the wall of 

a single segment. It 

is believed that in 

cases of this kind the 

integument acts as 

a tympanum or 

sounding board. 





Fig. 164. — Chordotonal organ 
of a larva of Chironomus 
(From Graber). 



Fig. 165. — Diagram 

representing the 

chordotonal organs 
of a larva of Chiro- 
nomus (After Gra- 
ber). 



h. THE CHORDOTONAL ORGANS OF LARV^ 

Chordotonal organs have been observed in so many larvae that 
we may infer that they are commonly present in larvse. These organs 
are very simple compared with those of certain adult insects, described 
later. Those figured in the preceding paragraphs will serve to illus- 
trate the typical form of larval chordotonal organs. Even in the more 
complicated ones, there are comparatively few scolopophores ; and, as 
a rule, they are not connected with specialized tympana, but extend 
between distant parts of the body-wall, which probably acts as a 
sounding board. 

In certain larvse, however, the scolopophores are attached to 
specialized areas of the body -wall. Hess ('17) has shown that the 
pleural discs of cerambycid larvee, which are situated one on each side 
of several of the abdominal segments, serve as points of attachment 
of scolopophores. 



C. THE CHORDOTONAL ORGANS OF THE LOCUSTID^ 

In the Locustidae there are highly specialized ears situated one on 
each side of the first abdominal segment. The external vibrating 



THE INTERNAL ANA TOMY OF INSECTS 



149 




Fig. 1 66. — Side view of a locust with the wings 
removed; /, tympanum. 



part of these organs, the tympanum, is conspicuous, being a thinned 
portion of the body-wall (Fig. i66). 

Closely applied to the 
inner surface of each 
tympanum (Fig. 167, T), 
there is a ganglion 
known as Muller's organ 
{go), first described by 
Miiller (1826). This gan- 
glion contains many 
ganglion-cells and scolopalae and is the termination of a nerve extend- 
ing from the central nervous system, the auditory nerve (w). Figure 
168 represents a section of Miiller's organ, showing the ganglion-cells 
and scolopalcE. 

Intimately associated with the Miiller's organ are two horny 
processes (Fig. 167,6' and m) and a pear-shaped vesicle (Fig. 167, hi)\ 
and near the margin 
of the tympanum, 
there is a spiracle 
(Fig. 167, St), which 
admits air to a space 
inside of the tympa- 
num, the tympanal 
air-chamber. 

As the nerve-end- 
ings in Miiller's or- 
gan are attached to 
the tympanum, it is 
a chordotonal organ 
of the integumental 
type; it is attached 
to a vibratile mem- 
brane, between two 
air-spaces. 




Fig. 167. — Ear of a locust, Caloptenus itallcus, seen from 
inner side; T, tympanum; TR, its border; o, u, two 
horn-like processes; bi, pear-shaped vesicle; n, audi- 
tory nerve; ga, terminal ganglion or Muller's organ; 
st, spiracle; M, tensor muscle of the tympanum (From 
Packard after Graber). 



d. THE CHORDOTONAL 
ORGANS OF THE 
TETTIGONIID^ AND 
OF THE GRYLLID^ 

In the long-horned grasshoppers and in the crickets, there is a pair 
of tympana near the proximal end of the tibia of each fore leg. In 



150 



AN INTRODUCTION TO ENTOMOLOGY 



--S 



many genera, these t}Tnpana are exposed and easily observed (Fig. 
169) ; but in some genera each is covered by a fold of the body-wall 

and is consequently within a cavity, 
which communicates with the out- 
side air by an elongated opening 
(Fig. 170, a and b). 

Within the legs bearing these 
tympana, there are complicated 
chordotonal organs. Very de- 
tailed accounts of these organs 
have been pubhshed by Graber 
('76), Adelung ('92) and Schwabe 
('06); in this place, for lack of 
space, only their more general 
features can be described. 

Figure 171 represents a longi- 
tudinal section of that part of a 
fore tibia of Decticus verrucivorus in 
which the chordotonal organs are 
situated, and Figure 172 represents 
a cross-section of the same tibia, 
passing through the tympana and 
s, s, scolo- ii^Q air-chambers formed by the 
folds of the body-wall. In the fol- 
lowing account the references, in most cases, are to both of these figures. 




Fig. 168. — Section of Mullet's organ 
ganglion-cells; n, nerve; 
palie (After Graber). 




Fig. 169. — Fore leg of a katydid; i, tympa- 
ntun. 




a 



Fig. 1 70. — Tibia of a locustid 
with covered tympana; a, 
front view; &, side view; 0, 
opening (After Schwabe). 



The trachea of the leg.— The trachea of the leg figured in part here 
is remarkable for its great size and for its division into two branches, 



THE INTERNAL ANATOMY OF INSECTS 



151 



the front trachea (Ti) and the hind trachea (Tc) ; these two branches 

reunite a short distance beyond the end cf the chordotonal organs. 

It is an interesting 
fact that these large 
tracheae of the legs 
containing the chor- 
dotonal organs open 
through a pair of 
supemumery spir- 
acles, differing in this 
respect from the tra- 
chea cf the other legs. 
The spaces cf the 
leg. — ^ By reference 
to Figure 172, it will 
be seen that the two 
branches of the leg 
trachea occupy the 
middle space of the 
leg between the two 
tympana (Tie and 
^ Tii) and separate an 
outer space, the upper 
one in the figure, from 
an inner space. The 
outer space (E) con- 
tains a chordotonal 
organ, of which the 
scolopale is repre- 
sented at S ; and the 
inner space contains 
small tracheae (t), 
muscles (m), the 
tibial nerve (Ntb), 
and a tendon (Tn). 
The interstices of the 
outer and inner spaces 
are filled with blood. 

In the outer space some leucocytes and fat-cells (Gr) are represented. 
The supra-tympanal or subgenual organ. — In the outer space of 

the tibia, a short distance above the tympana, there is a ganglion (Fig. 




Fig. 171. — Longitudinal section of a fore tibia of 
Decticus verrucivoms (From Berlese after Schwabe). 



152 



AN INTRODUCTION TO ENTOMOLOGY 



171, Os) composed of nerve-endings, which are scolopophores of the 
integumental type. Two nerves extend to this ganglion, one from 

each side of the leg, and 
each divides into many 
scolopophores. The 
attachment fibers of the 
scolopophores converge 
and are attached to the 
wall of the leg. Two 
terms have been applied 
to this organ, both indicat- 
ing its position in the leg; 
one refers to the fact that 
it is above the tympana, 
the other, that it is below 
the knee. 

The intermediate or- 
gan. — Immediately below 
Fig. 172.— Transverse section of the fore tibia of +>ip ^inra tvmnanfll nrran 
Decticus verrucivorus (From Berlese after the supra-tympanal organ, 
Schwabe). In comparing this figure with the and between it and the 
preceding, note that in that one the external ^^„^^ described in the next 
parts are at the left, in this one, at the right. °^g^^ aescriDea mtnenext 

paragraph, is a ganglion 
composed of scolopophores of the subintegumental type; this is 
termed the intermediate organ (Fig. 171, Oi). 

Siebold's organ or the crista acustica. — On the outer face of the 
front branch of the large trachea of the leg there is a third chordo- 
tonal organ, the Siebold's organ or the crista acustica. A surface view 
of the organ is given in Figure 171 and a cross-section is represented in 
Figure 172. It consists of a series of scolopophores of the subintegu- 
mental type, which diminish in length toward the distal end of the 
organ (Fig. 171). The relation of Siebold's organ to the trachea is 
shown in Figure 172. It forms a ridge or crest on the trachea, shown 
in setion at cr in Figure 172; this suggested the name crista acustica, 
used by some writers. 




e. THE Johnston's organ 

There has been found in the pedicel of the antenna of many insects, 
representing several of the orders, an organ of hearing, which is known 
as the Johnston's organ, having been pointed out by Christopher 
Johnston (1855). This organ varies somewhat in form in different 



THE INTERNAL ANATOMY OF INSECTS 



153 



insects and in the two sexes of the same species; but that of a male 
mosquito will serv^e as an example illustrating its essential features. 

The following 
account is 
based on an in- 
vestigation by 
Professor Ch. 
/ M. Child ('94). 
In an an- 
tenna of a mos- 
quito (Fig. 173) 
the scape or 
first segment, 
which contains 
the muscles of 
the antenna, is 
much smaller 
than the pedicel 
or second seg- 
ment, and is 
usually over- 
looked, being 
concealed b y 
the large, glob- 
ular pedicel; 
the clavola con- 
sists of thirteen 
slender seg- 
ments. Excepting one or two terminal segments, each segment of 
the clavola bears a whorl of long, slender setae; these are more 
prominent in the male than in the female. 

Figure 174 represents a longitudinal section of the base of an 
antenna; in this the following parts are shown: S, scape; P, pedicel, 
C, base of the first segment of the clavola; cp, conjunctival plate 
connecting the pedicel with the first segment of the clavola; pr, 
chitinous processes of the conjunctival plate; m, muscles of the 
antenna; N, principal antennal nerve; n, nerve of the clavola; 
immediately within the wall of the segments there is a thin layer 
of hypodermis; the lumen of the pedicel is largely occupied by a" 
ganglion composed of scolopophores, the attachment fibers of which 
are attached to the chitinous proce'-ses of the conjunctival plate. 




Fig. 173. — Antennas of mosquitoes, Culex; 
female; s, scape; p, pedicel. 



154 



AN INTRODUCTION TO ENTOMOLOGY 



As to the action of the auditory apparatus as a whole, it was shown 
experimentally by Mayer ('74) that the different whorls of setae borne 
by the segments of the clavola, and which gradually decrease in length 
on successive segments, are caused to vibrate by different notes ; and 
it is believed that the vibrations of the setse are transferred to the 
conjunctival plate by the clavola, and thence to the nerve-end- 
ings. 

It was formerly 
believed that the 
great specialization 
of the Johnston's or- 
gan in male mosqui- 
toes enabled the 
males to hear the 
songs of the females 
and thus more readily 
to find their mates. 
But it has been found 
that in some species, 
at least, of mosqui- 
toes and of midges 
in which the males 
have this organ high- 
ly specialized the fe- 
males seek the males. This has led some writers to doubt that the 
Johnston's organ is auditory in function. But the fact remains that 
its distinctive feature is the presence of scolopalae, which is the dis- 
tinctive characteristic of the auditory organs of other insects. 




Fig. 1 74. — Longitudinal section of the base of an anten- 
na of a male mosquito, Corethra culiciformis (After 

Child). 



XIV. SENSE-ORGANS OF UNKNOWN FUNCTIONS 

In addition to the sense-organs discussed in the foregoing account 
there have been described several types of supposed sense-organs 
which are as yet very imperfectly understood. Among these there is 
one that merits a brief discussion here on account of the frequent 
references to it in entomological literature. Many different names 
have been applied to the organs of this type; of these that of sense 
domes is as appropriate as any, unless the conclusions of Mclndoo, 
referred to on the following page, are confirmed, in which case his 
term olfactory pores will be more descriptive. 



THE INTERNAL ANATOMY OF INSECTS 



155 




a b 

Fig. 175. — Sense-domes (From Berlese). 



The sense-domes are found in various situations, but they occur 
chiefly on the bases of the wings and on the legs. Each sense-dome 
consists of a thin, hemispherical or more nearly spherical membrane, 

which either projects from the 
outer end of a pore in the 
cuticula (Fig. 175, a) or is 
more or less deeply enclosed 
in such a pore (Fig. 175, h)\ 
intergrades between the two 
types represented in the accom- 
panying figures occur. 

When a sense-dome is 
viewed in section a nerve- 
ending is seen to be connected 
with the dome-shaped or bell- 
like membrane. A striking 
feature of these organs is the 
absence of any gland -cells connected with them, such as are found 
in the chemical sense-organs described on an earlier page. 

In one very important respect there is a marked difference in the 
accounts of these organs that have been published. The organs were 
first discovered long ago by Hicks ('57); but they have been more 
carefully studied in recent years by several writers, who have been 
able to make use of a greatly improved histological technic; among 
these writers are Berlese (09 a), Vogel ('11), Hochreuter (12'), Lehr 
('14), and Mclndoo ('14). 

All of the writers mentioned above except the last named maintain 
that the sense-cell ends in a structure, in the middle of the sense-dome, 
which differs in appearance from both the membrane of the sense- 
dome and the body of the sense-cell. This 
structure varies in form in different sense- 
domes; in some it is cyHndrical, and is 
consequently described as a peg; in others, 
it is greatly flattened so that it is semilunar 
in form when seen in section. In Figure 
175, ^. which represents a section made 
transversely to the long axis of this part it 
appears peglike ; but in Figure 175,0, which 
represents a longitudinal view of it, it is 
semilunar in form. 

According to Mclndoo (Fig. 176) no structure of this kind is 




Fig. 176 — Olfactory pore 
of Mclndoo (From 
Mclndoo) 



156 AN INTROD UCTION TO ENTOMOLOG Y 

present, but the sense-fiber of the sense-cell pierces the bottom of the 
cone and enters the round, oblong, or slit-like pore-aperture. "It is 
thus seen that the cytoplasm in the peripheral end of the sense- 
fiber comes in direct contact with the air containing odorous par- 
ticles and that odors do not have to pass through a hard membrane 
in order to stimulate the sense-cell as is claimed for the antennal 
organs." 

XV. THE REPRODUCTIVE ORGANS 

a. THE GENERAL FEATURES 

In insects the sexes are distinct. Formerly Termitoxenia, a genus 
of wingless, very aberrant Diptera, the members of which live in nests 
of Termites, was believed to be hermaphroditic, but this is now 
doubted. 

Individuals in which one side has the external characters of the 
male and the other those of the female are not rare ; such an individual 
is termed a gyndndromorph; in some gynandromorphs, both testes 
and ovaries are present but in no case are both functional ; these there- 
fore are not true hermaphrodites. 

In females the essential reproductive organs consist of a pair of 
ovaries, the organs in which the ova or eggs are developed, and a tube 
leading from each ovary to an external opening, the oviduct. In the 
male, the essential reproductive organs are a pair of testes, in which 
the spermatozoa are developed and a tube leading from each testis to 
an external opening, the vas deferens. In addition to these essential 
organs, there are in most insects accessory organs, these consist of 
glands and of reservoirs for the reproductive elements. 

The form of the essential reproductive organs and the number and 
form of the accessory organs vary greatly in different insects. It is 
impossible to indicate the extent of these variations in the limited 
space that can be devoted to this subject in this work. Instead of 
attempting this it seems more profitable to indicate by diagrams, one 
for each sex, the relations of the accessory organs that may exist to 
the essential organs. 

In adult insects the external opening of the reproductive organs is 
on the ventral side of the abdomen near the caudal end of the body. 
The position of the opening appears to differ in different insects and in 
some cases in the two sexes of the same species. The lack of uni- 
formity in the published accounts bearing on this point is partly due 
to differences in numbering the abdominal segments; some authors 
describing the last segment of the abdomen as the tenth while others 



THE INTERNAL ANATOMY OF INSECTS 



157 



believe it to be the eleventh; embryological evidence supports the 
latter view. 

In most insects there is a single external opening of the reproduc- 
tive organs; but in the Ephemerida and in a few other insects the two 
efferent ducts open separately. 

Secondary sexual characters. — In addition to differences in the 
essential reproductive organs and in the genital appendages of the 
two sexes, many insects exhibit what are termed secondary sexual 
characters. Among the more striking of these are differences in size, 
coloring, and in the form of certain organs. Female insects are 
usually larger than the males of the same species; this is due to the 
fact that the females carry the eggs ; but in those cases where the males 



fight for their mates, as stag-beetles, the males are the larger. 

ing differences in the color- 
ing of the two sexes are 
common, especially in the 
Lepidoptera. In many 
insects the antennee of the 
male are more highly 
specialized than those of 
the female; and this is 
true also of the eyes of 
certain insects. These are 
merely a few of the many 
known secondary sexual 
characters found in insects. 



Strik- 




Fig. 178- 
Repro- 
ductive 
organs of 
Japyx, 
female 
(After 
Grassi) . 



b. THE REPRODUCTIVE 

ORGANS OF THE 

FEMALE 

The general features of 

^~. . - --^5^ the ovajy.— In the more 
^JJ^^ p^^^^^**^^^^s==^ usual form of the ovaries 
of insects, each ovary is 
a compact, more or less spindle- 
shaped body composed of many paral- 
lel ovarian tubes (Fig. 177, 0), which 
open into a common efferent tube, 
the oviduct. In CampoJ^a, however, 
there is a single ovarian tube; and in certain other Thysanura the 
ovarian tubes have a metameric arrangement (Fig. 178). The nvim- 



Fig. 177. — Diagram of thereproduc- 
tive organs of a female insect; 0, 
ovary; od, oviduct; c, egg-calyx; v, 
vagina; 5,spermatheca; 6c, bursa 
copulatrix; sg, spermathecal 
gland; eg, colleterial glands. 



158 



AN INTRODUCTION TO ENTOMOLOGY 



ber of ovarian tubes differs greatly in different insects; in many 
Lepidoptera there are only four in each ovary; in the honeybee, 
about 150; and in some Termites, 3000 or more. 

The wall of an ovarian tube..— The ovarian tubes are lined with 
an epithelial layer, which is supported by a basement membrane; out- 
side of this there is a peritoneal envelope, composed of connective tis- 
sue; and sometimes there are muscles in the peritoneal envelope. 
The zones of an ovarian tube. — Three different sections or zones are 
recognized in an ovarian tube; first, 
the terminal filament, which is the 
slender portion which is farthest from 
the oviduct (Fig. 179, /); second, the 
germarium, this is a comparatively short 
chamber, between the other two zones 
(Fig. 179, g); and third, the vitellarium, 
which constitutes the greater portion of 
the ovarian tube. 

The contents of an ovarian tube. — In 
the germarium are found the primordial 
germ-cells from which the eggs are devel- 
oped; and in the vitellarium are found 
the developing eggs. In addition to the 
cells that develop into eggs there are 
found, in the ovarian tubes of many 
insects, cells whose function is to furnish 
nutriment to the developing eggs; these 
are termed nurse-cells. 

Depending upon the presence cr ab- 
sence of nurse-cells and on the location of 
the nurse-cells when present, three types 
of ovarian tubes are recognized: first, 
those without distinct nurse-cells (Fig. 
1 79, A) ; second, those in which the eggs 
and masses of nurse-cells alternate in the 
ovarian tube (Fig. 179, B); and third, 
those in which the nurse-cells are 
restricted to the germarium (Fig. 179, C), which thus becomes a nutri- 
tive chamber. In the latter type the developing eggs are each con- 
nected by a thread with the nutritive chamber. 

The egg-follicles. — The epithelium lining of the ovarian tube 
becomes invaginated between the eggs in such a way that each egg is 




Fig. 179. — Three 

ovarian tubes; e, e, e, 
eggs; n, n, n, nurse-cells 
(After Berlese). 



THE INTERNAL ANA TOMY OF INSECTS 159 

enclosed in an epithelial sac or egg-follicle, which passes down the tube 
with the egg (Fig. 179). There is thus a tendency to strip the tube of 
its epithelium, but a new one is constantly formed. 

The functions of the follicular epithelium. — It is believed that in 
some cases, and especially where the nurse-cells are wanting, the 
follicular epithelium serves a nutritive function. Eut the most 
obvious function cf this epithelium is the formation cf the chorion or 
egg-shell, which is secreted on its inner surface. The pit-like mark- 
ings so common on the shells of insect eggs indicate the outlines of the 
cells of the follicular epithelium. 

The ligament of the ovary. — In many insects, the terminal fila- 
ments of the several ovarian tubes of an ovary unite and form a 
slender cord, the ligament of the ovary, which is attached to the dorsal 
diaphragm; but in other insects this ligament is wanting, the terminal 
filaments ending free in the body cavity. 

The oviduct. — The common outlet of the ovarian tubes is the ovi- 
duct (Fig. jj-j, od). In most insects the oviducts of the two ovaries 
unite and join a common outlet, the vagina; but in the Ephemerida 
and in some Dermaptera each oviduct has a separate opening. 

The egg-calyx. — In some insects each oviduct is enlarged so as to 
form a pouch for storing the eggs, these pouches are termed the egg- 
calyces (Fig. 177, c.) 

The vagina. — The tube into which the oviducts open is the vagina 
(Fig. 177, v). The vagina differs in structure from the oviducts, due 
to the fact that it is an invagination of the body-wall, and, like other 
invaginations of the body- wall, is lined with a cuticular layer 

The spermatheca. — The spermatheca is a sac for the storage of the 
seminal fluid (Fig. 177,5). As the pairing of the sexes takes place only 
once in most insects and as the egg-laying period may extend over a 
long time, it is essential that provision be made for the fertilization of 
the eggs developed after the union of the sexes. The eggs become full- 
grown and each is provided with a shell before leaving the ovarian 
tubes. At the time an egg is laid a spermatozoan may pass from the 
spermatheca, where thousands of them are stored, into the egg 
through an opening in the shell, the micropyle, which is described in 
the next chapter (Figs. 184 and 185). 

In some social insects, eggs that are developed years after the 
pairing took place are fertilized by spermatozoa that have been stored 
in the spermatheca. 

The bi'rsa copulatrix. — In many insects there is a pouch for the 
reception of the seminal fluid before it passes to the spermatheca. 



160 AN INTRODUCTION TO ENTOMOLOGY 

This pouch is known as the bursa copulatrix or copulatory pouch. In 
some insects this pouch is a diverticulimi of the vagina (Fig. 177, he); 
in others it has a distinct external opening, there being two external 
openings of the reproductive organs, the opening of the vagina and the 
opening of the bursa copulatrix. 

When the bursa copulatrix has a distinct external opening there 

may or may not be a passage from it to the vagina. In at least some 

Orthoptera (Melanoplus) there is no connection between the two; 

^^ when the eggs are laid they are 

w^ ^ — "J^^ »■ — V. pushed past the opening of the 

^^""V^'-''^ V-^"" bursa copulatrix where they are 

4/\ j^-^'.i ■5"'m^.-'#' fertilized. 

'^^''^f^^^^^^''^^^^S^^^^^m..o:r In the Lepidoptera (Fig. 180), 

Tj^n feB^^==£=:^E^^^i:^^ there is a passage from the bursa 

^' {^^dfjJ^-^'^ ^^^^^^^^^^^^^^^ copulatrix to the vagina. In 

J^§^-ov ^ this case the seminal fluid is 

Fig. i8o.-Reproductive organs of the I'eceived by the bursa copulatrix 
femaleof the milkweed butterfly; a, at the time of pairing, later it 
anus; ft, opening of the bursa copula- . .1^ Qnermathprfl anrl 

trix; ov, ovarian tubes; /, terminal passes to tne spermatneca, ana 
filaments of the ovary; v, opening from here it passes to the Vagina, 
of the vagina (After Burgess). ^ ^^^^^ copulatrix is said to 

be wanting in Hymenoptera, Diptera, Heteroptera and Homoptera 
except the Cicadas. 

The coUeterial glands.— There are one or two pairs of glands that 
open into the vagina near its outlet (Fig. 177, eg); to these has been 
applied the general term coUeterial glands. Their function differs in 
different insects ; in some insects they secrete a cement for gluing the 
eggs together, in others they produce a capsule or other covering 
which protects the eggs. 

The spermathecal gland. — In many insects there is a gland that 
opens either into the spermatheca or near the opening of the sperma- 
theca, this is the spermathecal gland (Fig. 177, sg). 

C. THE REPRODUCTIVE ORGANS OF THE MALE 

The reproductive organs of the male are quite similar in their more 
general features to those of the female; but there are striking differ- 
ences in details of form. 

The general features of the testes. — As the reproductive elements 
developed in the testes, the spermatazoa, always remain small, the 
testes of a male are usually much smaller than the ovaries of the female 
of the same species. 



THE INTERNAL ANATOMY OF INSECTS 



161 




In the more common form, each testis is a compact body (Fig. 
i8i, t) composed of a variable number of tubes corresponding with 
the ovarian tubes, these are commonly called 
the testicular follicles; but it would have been 
better to have termed them the testicular tubes, 
reserving the term follicle for their divisions. 

The testicular follicles vary in number, 
form, and in their arrangement. In many 
insects as the Neuroptera, the Hemiptera, the 
Diptera, and in Campodea and Japyx, each 
testis is composed of a single follicle. In some 
beetles, Carabidse and Elateridae, the follicle 
is long and rolled into a ball. In some Thy- 
sanura the testicular follicles have a metameric 
arrangement. 

In some Coleoptera, each testis is separated 
into several masses, each having its own outlet 
leading to the vas deferens; while in some 
other insects the two testes approach each other 
during the pupal stage and constitute in the 
adult a single mass. 

The structure of a testicular follicle. — Like 
the ovarian tubes, the testicular follicles are 
lined with an epithelial layer, which is sup- 
ported by a basement membrane, outside of 
which there is a peritoneal envelope composed 
And in these follicles a series of zones are 
distinguished in which the genital cells are found in different stages 
of development, corresponding to the successive generations of these 
cells. In addition to the terminal filament four zones are recog- 
nized as follows: 

The germarium. — This includes the primordial germ-cells and the 
spermatogonia. 

The zone of growth. — Here are produced the spermatocytes of the 
first order and the spermatocytes of the second order. 

The zone of division and reduction. — In this zone are produced the 
Spermatids or immature spermatozoa. 

The zone of transformation. — Here the spermatids become sper- 
matozoa. 

A discussion of the details of the development of the successive 
generations of the genital cells of the male, or spermatogenesis, does 
not fall within the scope of this volume. 



Fig. 1 8 1 . — D i agram of 
the reproductive or- 
gans of a male insect ; 
the right testis is shown 
in section; ag, acces- 
sory glands; ed, eja- 
culatory duct; ^i^, semi- 
nal vesicles; t, testes; 
vd, vasa deferentia. 

of connective tissue. 



162 AN INTRODUCTION TO ENTOMOLOGY 

The spermatophores. — In some insects the spermatozoa become 
enveloped in a sac in which they are transferred to the female; this 
sac is the spermatophore. Spermatophores have been observed in 
Gryllidse, Locustidae, and certain Lepidoptera. 

Other structures. — A ligament of the testis, corresponding to the 
ligament of the ovary, is often present ; the common outlet of the testi- 
cular follicles, corresponding to the oviduct is termed the vas deferens 
(Fig. i&i, vd); an enlarged portion of the vas deferens serving as a 
reservoir for the products of the testis is known as a seminal vesicle 
(Fig. i8i, sv); the invaginated portion of the body-wall, correspond- 
ing with the vagina of the female, is the ejaculatory duct (Fig. i8i, ed); 
accessory glands, corresponding to the colleterial glands of the female, 
are present (Fig. i8i, ag); the function of these glands has not been 
determined, they may secrete the fluid part of the semen, and they 
probably secrete the spermatophore when one is formed; the penis, 
this is merely the chitinized terminal portion of the ejaculatory duct, 
which can be evaginated with a part of the invaginated portion of the 
body-wall. It is furnished with powerful muscles for its protrusion 
and retraction. 

XVI. THE SUSPENSORIA OF THE VISCERA 

The organs discussed here do not constitute a well-defined system, 
but are isolated structures connected with 
different viscera. As in most cases they 
appear to serve a suspensory function, they 
are grouped together provisionally as the sus- 
pensoria of the viscera. 

The dorsal diaphragm. — This is a mem- 
branous structure which extends across the 
. _ , abdominal cavity immediately below the 

^. , heart, to which it is attached along its median 

-„. -Diagram shov/- 0^11.1 • <• ^1 • j- 1 

ing the relation of the hne. i he lateral margms 01 this diaphragm 

dorsal diaphragrn and are attached to the sides of the body by a 
the ventral diaphragm . . . , , . , • 1 1 

to other viscera; a, series of triangular prolongations, which have 

alimentary canal; d, been commonly known as the -wings of the 
dorsal diaphragm; h, , ,^. s ^1 -, 11-1 

heart; n, ventral nerv- heart (Fig. 139, c). The dorsal diaphragm IS 
ous system; v, ventral composed largely of very delicate muscles, 
diaphragm. ^ , . / , . .,, -, , .1 

Its relation to the heart is illustrated by the 

accompanying diagram (Fig. 182, d). 

There are differences of opinion as to the function of the dorsal 
diaphragm. An important function is probabh^ to protect the heart 




THE INTERNAL A NA TOM Y OF INSECTS 163 

from the peristaltic movements of the ahmentary canal. It also 
supports the heart; and it may play a part in its expansion. 

The dorsal diaphragm is also known as the pericardial diaphragm. 

The ventral diaphragm. — The ventral diaphragm is a very delicate 
membrane which extends across the abdominal cavity immediately 
above the ganglia of the central nervous system. It is quite similar 
in form to the dorsal diaphragm ; it is attached along each side of the 
body, just laterad of the great ventral muscles, by a series of pro- 
longations resembling in form the wings of the heart. The position of 
the ventral diaphragm is illustrated in Figure 182, v. 

This diaphragm has been described as a ventral heart; but I 
believe that its function is to protect the abdominal ganglia of the 
central nervous system from the peristaltic movements of the alimen- 
tary canal. 

The thread-like suspensoria of the viscera. — Under this head may 
be classed the ligament of the ovary and the ligament of the testis, 
already described. In addition to these, there is, in some insects at 
least, a thread-like ligament that is attached to the intestine. 

XVII. SUPPLEMENTARY DEFINITIONS 

There are found in the bodies of insects certain organs not referred 
to in the foregoing general account of the internal anatomy of insects. 
These organs, though doubtless very important to the insects in which 
they occur, are not likely to be studied in an elementary course in 
entom-ology and, therefore, a detailed account of them may well be 
omitted from an introductory text -book. This is especially true as 
our knowledge of the structure and functions of these organs is so 
incomplete that an adequate discussion of the conflicting views now 
held v/ould require more space than can be devoted to it here. The 
organs in question are the following : 

The oenocytes. — The term cenocytes is applied to certain very large 
cells, that are found in clusters, often metamerically arranged, and 
connected with the tracheae and the fat body of insects. The name 
was suggested by the light yellow color which often characterizes 
these cells, the color of certain wines; but the name is not a good one, 
as oenocytes vary greatly in color. Several other names have been 
applied to them but they are generally known by the name used here. 
Two types of oenocytes are recognized: first, the larval oenocytes; 
and second, the imaginal oenocytes. 



164 AN INTRODUCTION TO ENTOMOLOGY 

The lar\^al oenocytes are believed by Verson and Bisson ('91) to be 
ductless glands which take up, elaborate, and return to the blood 
definite substances, which may then be taken up by other cells of the 
body. Other views are held by other writers, but the view given 
above seems, as this time to be the one best supported by the evidence 
at hand. 

As to the function of the imaginal oenocytes, there are some obser- 
vations that seem to show that they are excretory organs without 
ducts, cells that serve as storehouses for excretory products, becoming 
more filled with these products with the advancing age of the insect. 

The pericardial cells. — The term fericardial cells is applied to a 
distinct type of cells that are found on either side of the heart in the 
pericardial sinus or crowded between the fibers of the pericardial 
diaphragm. 

These cells can be rendered very conspicuous by injecting ammonia 
carmine into the living insect some time before killing and dissecting 
it ; by this method the pericardial cells are stained deeply while the 
other cells of the body remain uncolored. 

It is believed that the pericardial cells absorb albuminoids origina- 
ting from the food and transform them into assimilable substances. 

The phagocytic organs. — The term phagocyte is commonly applied 
to any leucocyte or white blood corpuscle that shows special activity 
in ingesting and digesting waste and harmful materials, as disinte- 
grating tissue, bacteria, etc. The action of phagocytes is termed 
phagocytosis; an excellent example of phagocytosis is the part played 
by the leucocytes in the breaking down and rebuilding of tissues in the 
course of the metamorphosis of insects ; this is discussed in the next 
chapter. 

Phagocytosis may take place in any part of the body bathed by the 
blood and thus reached by leucocytes. In addition to this widely 
distributed phagocytosis, it is beheved that in certain insects there are 
localized masses of cells which perform a similar function; these 
masses of cells are known as the phagocytic organs. 

Phagocytic organs have been found in many Orthoptera and in 
earwigs; they are situated in the pericardial region; and can be made 
conspicuous by injecting a mixture of ammonia carmine and India ink 
into the body cavity; by this method the pericardial cells are stained 
red and the phagocytic organs black. 

The light-organs. — The presence of organs for producing light is 
widely distributed among living forms both animal and vegetable. 



THE INTERNAL ANA TOMY OF INSECTS 165 

The most commonly observed examples of light-producing insects are 
certain members of the Lampyridas, the fireflies and the glow-worms, 
and a member of the Elateridas, the "cucujo" of the tropics. With 
these insects the production of light is a normal function of highly 
specialized organs, the light-organs. 

Examples of insects in which the production of light is occasionally 
observed are larvee of mosquitoes, and certain lepidopterous larvae. 
In these cases the production of light is abnormal, being due either to 
the presence in the body of light-producing bacteria or to the ingestion 
of luminescent food. 

The position of the specialized light-organs of insects varies 
greatly; in the fireflies, they are situated on the ventral side of the 
abdomen; in the glow-worms, along the sides of the abdomen; and in 
the cucujo, the principal organs are in a pair of tubercles on the dorsal 
side of the prothorax and in a patch in the ventral region of the 
metathorax. 

The structure of the light-organs of insects varies in different 
insects, as is shown by the investigations of several authors. A good 
example of highly specialized light-organs are those of Photinus 
marginellus, one of our common fireflies. An excellent account of 
these is that of Miss Townsend ('04), to which the reader is referred. 
A detailed account of the origin and development of the light-organs 
of Photurus pennsylvanica is given by Hess ('22). 



CHAPTER IV. 
THE METAMORPHOSIS OF INSECTS 

Many insects in the course of their lives undergo remarkable 
changes in form ; a butterfly was once a caterpillar, a bee lived first the 
life of a climisy footless grub, and flies, which are so graceful and activ e, 
are developed from maggots. 

In the following chapters considerable attention is given to 
descriptions of the changes through which various insects pass; the 
object of this chapter is merely to discuss the more general features of 
the metamorphosis of insects, and to define the terms commonly used 
in descriptions of insect transformations. 

I. THE EXTERNAL CHARACTERISTICS OF THE META- 
MORPHOSIS OF INSECTS 

The more obvious characteristics of the metamorphosis of insects 
are those changes in the external form of the body that occur during 
postembryonic development. In some cases there appears to be but 
little in common between the successive forms presented by the same 
insect, as the caterpillar, chrysalis, and adult stages of a butterfly. 
On the other hand, in certain insects, the change in the form of the 
body during the postembryonic life is comparatively little. Based 
on these differences, several distinct types of metamorphosis have 
been recognized; and in those cases where the insect in its successive 
stages assumes different forms, distinctive terms are applied to the 
different stages. 

a. THE EGG 

Strictly speaking, all insects are developed from eggs, which are 
formed from the primordial germ-cells in the ovary of the female. 
As a rule, each egg is surrounded by a shell, formed by the follicular 
epithelium of the ovarian tube in which the egg is developed; and 
this egg, enclosed in its shell, is deposited by the female insect, usually 
on or near the food upon which the young insect is to feed. In some 
cases, however, the egg is retained by the female until it is hatched; 
thus flesh-flies frequently deposit active larvag upon meat, especially 
when they have had difficulty in finding it; and t'.ere are other vivi- 
parous insects, which are discussed later. In tl" ! s place is discussed 

(166) 



THE METAMORPHOSIS OF INSECTS 



167 




the more common type of insect eggs, those that are laid while still 

enclosed in their shell. 

The shape of the egg. — The terms ovoid and ovate have a definite 

meaning which has been derived from the shape of the eggs of birds ; 

but while many eggs of 
insects are ovate in form, 
many others are not. 

The more common 
form of insect eggs is 
an elongate oval, some- 
what curved; this type is 
illustrated by the eggs 
of crickets (Fig. 183, i); 
many eggs; are approx- 
imately spherical, as those 
of some butterflies (Fig. 
183, 2) ; while some are of 
remarkable shape, two of 
these are represented in 
Figure 183,3, 4. 

The sculpture of the 
shell. — Almost always the 
external surface of the shell 
gonal areas; these are the 




Fig. 183. — Eggs of insects; 1 , CEcanthus nigri- 
cornis; 2, CEnis semidea; 3, Piezoslerum 
subidatum; 4, Hydromeira martini. 



of an insect egg is marked with small, hex 
imprints of the cells of the follicular epi- 
thelium, which formed the shell. In 
many cases the ornamentation of the 
shell is very conspicuous, consisting of 
prominent ridges or series of tubercles ; 
this is well -shown in the eggs of many 
Lepidoptera (Fig. 184). 

The micropyle. — It has been shown, 
in the course of the discussion of the 
reproductive organs of the female, that 
the egg becomes full-grown, and the 
protecting chorion or egg-shell is formed 
about it before it is fertilized. This 
renders necessary some provision for the 
entrance of the male germ -cell into the 
egg; this provision consists of one or 
more openings in the shell through which a spermatozoan may enter. 
This opening or group of openings is termed the micropyle. 




Fig. 184.— Egg of the cotton- 
worm moth; the micropyle is 
shown in the center of the lower 
figure. 



168 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. 185.— Egg 
Drosophila melan- 
ogaster; m, micro- 
pyle. 



The number and position of the micropylar openings varies greatly 
in the eggs of different insects. Frequently they present an elaborate 
pattern at one pole of the egg (Fig. 184); and sometimes they open 
through more or less elongated papillae (Fig. 185). 

While in most cases it is necessary that an egg be fertilized in order 
that development may continue, there are many instances of par- 
thenogenesis among insects. 

The number of eggs produced by insects. — 
A very wide variation exists in the number of 
eggs produced by insects. In the sheep-tick, for 
example, a single large egg is produced at a time, 
and but few are produced during the life of the 
insect; on the other hand, in social insects, as 
ants, bees, and termites, a single queen may 
produce hundreds of thousands of eggs during 
her lifetime. 

These, however, are extreme examples; the 
peculiar mode of development of the larva of the 
sheep-tick within the body of the female makes 
possible the production of but few eggs; while 
the division of labor in the colonies of social insects, by which the func- 
tion of the queen is merely the production of eggs, makes it possible 
for her to produce an immense number ; this is especially true where 
the egg-laying period of the queen extends over several years. 

The following may be taken as less extreme examples. In the 
solitary nest-building insects, as the fossores, the solitary wasps, and 
the solitary bees, the great labor involved in making and provisioning 
the nest results in the reduction of the number of eggs produced to a 
comparatively small number; while many insects that make no pro- 
vision for their young, as moths, for example, may lay several 
hundred eggs. 

With certain chalcis-flies the number of young produced is not 
dependent upon the number of eggs laid ; for with these insects many 
embryos are developed from a single egg. This type of development 
is termed polyembryony. 

Modes of laying eggs. — Perhaps in no respect are the wonderful 
instincts of insects exhibited in a more remarkable way than in the 
manner of laying their eggs. If insects were reasoning beings, and if 
each female knew the needs of her young to be, she could not more 
accurately make provision for them than is now done by the great 
majority of insects. 



THE METAMORPHOSIS OF INSECTS 



169 



This is especially striking where the life of the young is entirely 
different from that of the adult. The butterfly or moth may sip 
nectar from any flower; but when the female lays her eggs, she selects 
with unerring accuracy the particular kind of plant upon which her 
larvae feed. The dragonfly which hunts its prey over the field, returns 
to water and lays her eggs in such a position that the young when it 
leaves the egg is either in or can readily find the element in which 
alone it is fitted to live. 

The ichneumon-flies frequent flowers; but when the time comes 
for a female to lay her eggs, she seeks the particular kind of larva 
upon which the species is parasitic, and will lay her eggs in no other. 
It' is a remarkable fact that no larva leads so secluded a life that it 
cannot be found by its parasites. Thus the larvae of Tremex columba 
bore in solid wood, where they are out of sight and protected by a 
layer of wood and the bark of the tree in which they are boring; 

nevertheless the ichneumon-fly 
Megarhyssa lunator, which is 
parasitic upon it, places her eggs 
in the burrows of the Tremex by 
means of her long drill-like 
ovipositor (Fig. i86). 

In contrast with the exam- 
ples just cited, some insects 
exhibit no remarkable instinct 
in their egg-laying. Our com- 
mon northern walking-stick, 
Diapheromera, drops its eggs on 
the ground under the shrubs 
and trees upon which it feeds. 
This, however, is sufficient pro- 
vision, for the eggs are pro- 
tected throughout the winter by 
the fallen leaves, and the young when hatched, readily find their food. 
Many species, the young of which feed upon foliage, lay their eggs 
singly upon leaves; but many others, and this is especially tine of 
those, the young of which are gregarious, lay their eggs in clusters. 
In some cases, as in the squash bug, the mass of eggs is not protected 
(Fig. 187) ; in others, where the duration of the egg-state is long, the 
eggs are protected by some covering. The females of our tent- 
caterpillars cover their eggs with a water-proof coating; and the 
tussock moths of the genus Hemerocampa covertheir egg-clusters with 
a frothy mass. 




Fig. 186. — Megarhyssa lunator. 



170 



AN INTRODUCTION TO ENTOMOLOGY 



The laying of eggs in compact masses, however, is not correlated, 
in most cases, with gregarious habits of the larvas. The water- 
scavenger beetles, Hydrophilidae, make egg-sacks out of a hardened 



silk-like secretion (Fig. i! 



the locusts, Acridiidas, lay their eggs in 
oval masses and cover them with a 
tough substance; the scale-insects 
of the genus Puhinaria excrete a 
large cottony egg-sac (Fig. 189); 



^^ 






Fig. 187 — Egg-mass of the 
squash-bug. 




Fig. 188. — Egg-ssLCot Hydrophilus 
(After Miall). 




Fig. 189. — Pulvinan'atnnumerabUis, females on 
grape with egg sacb 



the eggs of the praying mantis are laid in masses and overlaid with 
a hard covering of silk (Fig. igo) ; and cockroaches produce pod-like 
egg-cases, termed 
ootheca, each 
containing many 
eggs (Fig. 191). 

Among the 
more remarkable 
of the methods of 
caring for eggs is 

that of the lace-winged flies, Chrysopa. These insects place 
each of their eggs on the summit of a stiff stalk of hard silk 
(Fig. 192). 

Duration of the egg-state. — In the life-cycle of most insects, 
a few days, and only a few, intervene between the laying of 
an egg and the emergence of the nymph, naiad, or larva from 
it. In some the duration of the egg-state is even shorter, the 
hatching of the egg taking place very soon after it is laid, or 
pray- even, as sometimes in flesh-flies, before it is laid. On the 
m a i> *^^^*^^ hand, in certain species, the greater part of the life of an 
tis. individual is passed within the egg-shell. The common 
apple-tree tent-caterpillars, Clisiocampa americana, lays 
its eggs in early summer; but these eggs do not hatch till the fol- 
lowing spring ; while the remainder of the life-cycle occupies only a 



i:)D. 



o f 



THE METAMORPHOSIS OF INSECTS 



171 



few weeks. The eggs of Bittacus are said to remain unhatched for 
two years; and a similar statement is made regarding the eggs of 
our common walking-stick. 



b. THE HATCHING OF YOUNG INSECTS 

Only a few accounts have been published 

■regarding the manner in which a young insect 

frees itself from the embryonic envelopes. In ^'^cockmad?!^^''''^ °^ ^ 

some cases it is evident that the lar\^a cuts its 

way out from the egg-shell by means of its mandibles ; but in others, a 

specialized organ has been developed for this purpose. 

The hatching spines. — 
An organ for rupturing 
the embryonic envelopes 
is probably commonly pre- 
sent. It has been des- 
cribed under several 
names. It was termed an 
egg-burster by Hagen, the 
niptor ovi by C. V. Riley 
an egg-tooth by Heymons, 
and the hatching spines 
by Wheeler. 




Fig. 192. — Eggs, larva, cocoon, and adult of 
Chrysopa. 



C. THE MOLTING OF INSECTS 

The young of insects 
cast periodically the outer 
parts of the cuticula; this process is termed molting or ecdysis. 

General features of the molting of insects.— The chitinization of 
the epidermis or primary cuticula adds to its efficiency as an armor, but 
it prevents the expansion of the body-v/all rendered necessary by the 
growth of the insect; consequently as the body grows, its cuticula 
becomes too small for it. When this occurs a second epidermis is 
formed by the hypodermis; after which the old epidermis splits open, 
usually along the back of the head and thorax, and the insect works 
itself out from it. The new epidermis being elastic, accommodates 
itself to the increased size of the body ; but in a short time it becomes 
chitinized; and as the insect grows it in turn is cast off. The cast 
skin of an insect is termed the exuvice, the plural noun being used as in 
English is the word clothes. 



172 AN INTRODUCTION TO ENTOMOLOGY 

Coincident with the formation of the new epidermis, new setae 
are formed beneath the old epidermis; these He closely appressed to 
the outer surface of the new epidermis until released by the molting 
of the old epidermis. 

In the above account only the more general features of the process of molting 
are indicated, the details, according to the observations of Tower ('06) are as 
follows. (See Figure 1 13, p. 99). In the formation of the new epidermis it appears 
as a thin, delicate lamella, spread evenly over the entire outer surface of the 
hypodermis; it grows rapidly in thickness until finally, just before ecdysis takes 
place, it reaches its final thickness. After ecdysis the epidermis hardens rapidly 
and its coloration is developed. As soon as ecdysis is over the deposition of the 
dermis or secondary cuticula begins. This layer is a carbohydrate related 
to cellulose, and is deposited in layers of alternating composition, through the 
period of reconstruction and growth, during which it reaches its maximum thick- 
ness. Preliminary to ecdysis a thin layer of molting fluid is formed, and through 
its action the old dermis is corroded and often almost entirely destroyed, thus 
facilitating ecdysis. This dissolving of the dermis, is, according to Tower, a most 
constant phenomenon in ecdysis and has been found in all insects examined by 
him in varying degrees. 

It is said that the Collembola molt after reaching sexual maturity, 
in this respect agreeing with the Crustacea and the "Myriapoda," and 
differing from the Arachnida and from all other insects (Brindley '98). 

The molting fluid. — As indicated above, the process of molting is 
facilitated by the excretion of a fluid known as the molting fluid. This 
is produced by unicellular glands (Fig. 1 13, p. 99) which are modified 
hypodermal cells. These glands are found all through the life of the 
insect and upon all parts of the body; but are most abundant upon 
the pronotum, and are more abundant at pupation than at any other 
period. 

The number of postembryonic molts. — A very wide range of vari- 
ation exists as to number of molts undergone by insects after they 
leave the egg-shell. According to Grassi ('98, p. 292), there is only a 
single partial molt with Campodea and Japyx, while the May-fly 
Chloeon molts twenty times. Between these extremes every condition 
exists. Probably the majority of insects molt from four to six times ; but 
there are many records of insects that molt many more times than this. 

Stadia. — The intervals between the ecdyses are called stadia. In 
numbering the stadia, the first stadium is the period between hatching 
and the first postembryonic ecdysis. 

Instars. — The term instar is applied to the form of an insect during 
a stadium; in numbering the instars, the form assumed by the insect 
between hatching and the first postembryonic molt is termed the first 
instar. 



THE METAMORPHOSIS OF INSECTS 173 

Head measurements of larvse. — It was demonstratedby Dyar ('90) 
that the widths of the head of a larva in its successive instars follow 
a regular geometric progression in their increase. The head was 
selected as a part not subject to growth during a stadium; and the 
width as the most convenient measurement to take. By means of 
this criterion, it is possible to determine, when studying the transfor- 
mations of an insect, whether an ecdysis has been overlooked or not. 
Experience has shown that slight variations between the computed 
and the actual widths may occur; but these differences are so slight 
that the overlooking of an ecdysis can be readily discovered. The 
following example will serve to illustrate the method employed. 

A lan^a of Papilio thoas was reared from the egg; and the widths 
of the head in the successive instars was found to be, expressed in 
milhmeters, as follov/s: .6; i.i; 1.6; 2.2; 3.4. 

By dividing 2.2. by 3.4 (two successive members of this series), the 
ratio of increase was found to be .676+ ; the number, .68 was taken, 
therefore, as sufficiently near the ratio for practical purposes. By 
using this ratio as a factor the following results were obtained: 

Width foimd in fifth instar = 3.4 

Calculated width in fourth instar (3.4 X .68) = 2.312 

" "third " (2.312 X .68) =... . 1.57 

" " " second " (1.57 X .68) = 1.067 

" " first (1.067 X .68) = 72s 

By comparing the two series, as is done bslow, so close a correspond- 
ence is found that it is evident that no ecdysis was overlooked. 
Widths found: — .6; i.i; 1.6; 2.2; 3.4 
" calculated: — .7; 1.1-; 1.6-; 2.3. 

The reproduction of lost limbs. — The repro- 
duction of lost limbs has been observ^ed in many 
insects ; but such reproduction occurs here much 
less frequently than in the other classes of the 
Arthropoda. The reproduction takes place dur- 
ing the period of ecdysis, the reproduced part 
becoming larger and larger with each molt; 
hence with insects, and with Arachnida as well, 
the power of reproducing lost limbs ceases with 
the attainment of sexual maturity; but not so 
with the Crustacea and the "Myriapoda" which 
molt after becoming sexually mature. In none 

Fig. 93-— A spider in Qf ^he observed examples of the reproduction 
which lost legs we: e . , , ^- 1 1 j j 

being reproduced of appendages has an entire leg been reproduced. 




174 AN I NT ROD UCTION TO ENTOAIOLOCY 

It appears to be necessary that the original coxa be not removed in 
order that the reproduction may take place. Figure 193 represents 
a spider in our collection in which two legs, the left fore leg and the 
right hind leg, were being reproduced when the specimen was captured. 

d. DEVELOPMENT WITHOUT METAMORPHOSIS 

(Anietabolous* Development) 

While most insects undergo remarkable changes in form during 
their postembryonic development, there are some in which this is 
not the case. In these the young insect just hatched from the egg is 
of practically the same form as the adult insect. These insects grow 
larger and may undergo slight changes in form of the body and its 
appendages; but these changes are not sufficiently marked to merit 
being termed a metamorphosis. This type of development is known 
technically as ametdholoiis development. 

Development without metamorphosis is characteristic of the two 
orders Thysanura and Collembola, which in other respects, also, are 
the most generalized of insects. 

The nature of the changes in form undergone by an insect with an ametabolous 
development is iUustratcd by the development of Machilis alternata, one of the 
Thysanura. The first instar of this insect, according to Heymons ('07), lacks 
the clothing of scales, the styli on the thoracic legs, and the lateral rows of eversi- 
ble sacs on the abdominal segments; and the antennae and cerci are relatively 
shorter and consist of a much smaller rumber of segments than those of the adult. 
These changes, however, are comparable with those undergone by many animals 
in the course of their development that are not regarded as having a metamorpho- 
sis. In common usage in works on Entomology the term metamorphosis is used 
to indicate those m^arked changes that take place in the appearance of an insect 
that are correlated with the development of wings. 

In addition to the Thysanura and the Collembola there are certain 
insects that develop without metamorphosis, as the Mallophaga 
and the Pediculida^. But their ametabolous condition is believed to be 
an acquired one. In other words, it is believed that the bird-lice and 
the true Hce are descendants of winged insects whose form of body and 
mode of development have been modified as a result of parasitic life. 
The Ametabola. — Those insects that develop without meta- 
morphosis are sometim.es referred to as the Ametabola. This term was 
first proposed by Leach (18 15), who included under it the lice as well 
as the Thysanura and Collembola. But with our present knowledge, if 
it is used it should be restricted to the Thysanura and Collembola, 
those insects in which a development without metamorphosis is a 
primitive not an acquired conditicn. 

*Ametabolous: Greek a, without; metabole (fieTa^o\-n), change. 



2 HE METAMORPHOSIS OF INS.iCTS 



175 



e. GRADUAL METAMORPH ) IS 

{Paurometaboloits* Development) 

In several orders of insects there exists a type of development that 
is characterized by the fact that the young resemble the adult in the 
general form ot the body and in manner of life. There is a gradual 
growth of the body and of the wing rudiments and genital appendages. 




Fig. 194. — Nymph of Mela- 
noplus, first instar (After 
Emerton). 




Fig. 195. — Nymph of Mela- 
noplus, second instar 
(After Emerton). 




Fig. 196. — Nymph of Melano- 
plus, third instar (After Emer- 
ton) 




Fig, 198. — Nymph of Melano- 
plus, fifth instar (After Emer- 
ton), 




Fig. 197. — Nymph of Melano- 
plus, fourth instar (After 
Emerton). 




Fig. 199. — Melanoplus, 
adult. 



But the changes in form take place gradually and are not very great 
between any two successive instars except that at the last ecdysis 
there takes place a greater change, especially in the wings, than at 
any of the preceding ecdyses. This type of metamorphosis is desig- 
nated as gradual metamorphosis or paurometabolous development. 

The characteristic features oi paurometabolous development are 
correlated with the fact that the mode of life of the young and of the 



*Paurometabolous : pauros (TraCpos), little; nietahole {fiera^o'Ki^)^ change. 



176 AN INTROD UCTION TO ENTOMOLOG Y 

adult are essentially the same; the two living in the same situation, 
and feeding on the same food. The adult has increased power of loco- 
motion, due to the completion of the development of the wings; this 
enables it to more readily perform the functions of the adult, the 
spread of the species, and the making of provision for its continuance; 
but otherwise the life of the adult is very similar to that of the young. 

The development of a locust or short-homed grasshopper will 
serve as an example of gradual metamorphosis. Each of the instars 
of our common red-legged locust, Alclanoplus feniur-rtibrttm, is repre- 
sented in the accompanying series of figures. The adult (Fig. 199) 
is represented natural size; each of the other instars somewhat 
enlarged; the hair line above the figure in each case indicates the 
length of the insect. 

The young locust just out from the egg-shell can be easily recog- 
nized as a locust (Fig. 194). It is of course much smaller than the 
adult ; the proportion of the different regions of the body are some- 
what different ; and it is not furnished with wings ; still the form of the 
body is essentially the same as that of the adult. In the second and 
third instars (Fig. 195 and 196) there are sHght indications of the 
development of wing-rudiments; and these rudimentary wings are 
quite conspicuous in the fourth and fifth instars (Fig. 197 and 198). 
The change at the last ecdysis, that from the fifth instar to the adult, 
is more striking than that at any preceding ecdysis ; this is due to the 
complete expansion of the wings, which takes place at this time. 

The Paurometabola, — Those orders of insects that are characterized 
by a gradual metamorphosis are grouped together as the Paurometa- 
bola. This is not a natural division of the class Hexapoda but merely 
indicates a similarity in the nature of the metamorphosis in the orders 
included. This group includes the Isoptera, Dermaptera, Orthop- 
tera, Corrodentia, Thysanoptera, Homoptera, and Hemiptera. 

The term nymph. — An immature instar of an insect that undergoes 
a gradual metamorphosis is termed a nymph. 

In old entomological works, and especially in those written in the 
early part of the last century, the term nymph was used as a synonym 
of pupa ; but in more recent works it is applied to the immature instar 
of insects that undergo either a gradual or incomplete metamorphosis. 
In this book I restrict the use of this term to designate an immature 
instar of an insect that undergoes a gradual metamorphosis. 

Deviation from the usual type. — It is to be expected that within so 
large a group of organisms as the Paurometabola there should have 



THE ME TA MORPHOSIS OF INSECTS 177 

been evolved forms that exhibit deviations from the usual type of 
development. The more familiar examples of these are the following: 
The Saltatorial Orthoptera. — In the crickets, locusts, and long- 
homed grasshoppers, the wings of the nymphs are developed in an 
inverted position ; that surface of the wing which is on the outside in 
the adult is next to the body in the nymphal instars; and the rudi- 
mentary hind wings are outside of the fore wings, instead of beneath 
them, as in the adult. At the last ecdysis the wings assume the normal 
position. 

The Cicadas. — In the Cicadas there exists a greater difference 
between the nymphal instars and the adult than is usual with insects 
in which the metamorphosis is gradual. The nymphs live below the 
surface of the ground, feeding upon the roots of plants; the adults 
live in the open air, chiefly among the branches of trees. The forelegs 
of the nymphs are fossorial (Fig. 200) ; this is an 
adaptation for subterranean life, which is not needed 
and not possessed by the adults. And it is said that 
the last nymphal instar is quiescent for a period. 

The CoccidcB. — In the Coccidae the mode of devel- 
opment of the two sexes differ greatly. The female 
never acquires wings, and in so far as external form is 
concerned the adult is degenerate. The male, on 
the other hand, exhibits a striking approach to com- 
plete metamorphosis, the last nymphal instar being 
enclosed in a cocoon, and the legs of the adult are not 
those of the nymph, being developed from imaginal 
Pig. 200. — disks. But the wings are developed externally. 
^iSdai After ^^^ AleyrodidcB.—ln this family the type of meta- 
Riley). morphosis corresponds quite closely with that 

described later as complete metamorphosis; con- 
sequently the term larva is applied to the immature instars except 
the last, which is designated the pupa. 

The wings arise as histoblasts in the late embryo, and the growth 
of the wing-buds during the larval stadia takes place inside the body- 
wall. The change to the pupal instar, in which the wing-buds are 
external, takes place beneath the last larval skin, which is known as 
the pupa case or puparium. The adult emerges through a T-shaped 
opening on the dorsum of the puparium. Both sexes are winged. 

The Aphididce. — In the Aphididae there exists a remarkable type 
of development known as heterogamy or cyclic reproduction. This is 
characterized by an alternation of several parthenogenetic generations 




178 



AN INTRODUCTION TO ENTOMOLOGY 



with a sexual generation. And within the series of parthenogenetic 
forms there may be an alternation of winged and wingless forms. In 
some cases the reproductive cycle is an exceedingly complicated one ; 
and different parts of it occur on different food plants. 

The Thysanoptera. — In the Thysanoptera, as in most other insects 
with a gradual metamorphosis, the nymphs resemble the adults in the 
form of the body, and the wings are developed externally; but the last 
nymphal instar is quiescent or nearly so and takes no nourishment. 
This instar is commonly described as the pupa. 

/. INCOMPLETE METAMORPHOSIS 

(Hemimetabolous* Development) 

In three of the orders of insects, the Plecoptera, Ephemerida, and 
Odonata, there exists a type of metamorphosis in which the changes 




Fig. 20I 



-Transformation of a May-fly, Ephemera varia; A, 
adult; B, naiad (After Needham). 



that take place in the form of the body are greater than in gradual 
metamorphosis but much less marked than in complete metamorpho- 
sis. For this reason the terms incomplete metamorphosis and hemi- 
metaboloiis development have been applied to it. 

Both incomplete metamorphosis and complete metamorphosis are 
characterized by the fact that the immature instars exhibit adaptive 
modifications of form and structure, fitting them for a very different 
mode of life than that followed by the adult. This is often expressed 
by the statement that the im.mature instars are "sidewise developed" ; 
for it is believed that in these cases the development of the individual 
does not repeat the history of the race to which the individual belongs. 

*Hemimetabolous : hemi {vM-^), half; metabole (/ucto^oX'^), change. 



THE ME TA MORPHOSIS F INSECTS 1 79 

This mode of development is termed cenogenesis* It contrasts 
strongly with gradual metamorphosis, where there is a direct develop- 
ment from the egg to the adult. 

In each of the orders that are characterized by an incomplete 
metamorphosis, the adaptive characteristics of the young insects fit 
them for aquatic life; while the adults lead an aerial existence. The 
transformations of a May-fly (Fig. 201) will serve to illustrate this 
type of metamorphosis. 

The primitive insects were doubtless terrestrial ; this is shown by 
the nature of the respiratory system, which is aerial in all insects. In 
the course of the evolution of the different orders of insects, the 
immature forms of some of them invaded the water in search of food. 
This resulted in a sidewise development of these immature forms to 
better fit them to live in this medium; while the adult continued their 
development in, what may be termed by contrast, a direct line. In 
some of the Plecoptera, as Capnia and others, the results of the ceno- 
genetic development are not marked except that the immature forms 
are aquatic. 

In the three orders in which the metamorphosis is incomplete, the 
cenogenetic development of the immature instars involved neither a 
change in the manner of development of the wings nor a retarding of 
the development of the compound eyes; consequently these immature 
forms, although sidewise developed, constitute a class quite distinct 
from larvae. 

The Hemimetabola. — The three orders in which the development 
is a hemimetabolous one are grouped together as the Hemimetabola; 
these are the Plecoptera, Ephemerida, and Odonata. This grouping 
together of these three orders is merely for convenience in discussions 
of types of metamorphosis and does not indicate a natural division of 
the class Hexapoda. The radical differences in the three types of 
aquatic respiratory organs characteristic of the three orders indicate 
that they were evolved independently. 

The term naiad. — The immature instars of insects with an incom- 
plete metamorphosis have been termed nymphs; but as a result of 
their sidewise development they do not properly belong in the same 
class as the immature instars of insects with a gradual metamorphosis. 
I, therefore, proposed to designate them as naiads (Comstock '18, h). 

The adoption of the term naiad in this sense affords a distinctive 
term for each of the three classes of immature insects corresponding to 
the three types of metamorphosis, i. e., nymphs, naiads, and larvae. 



"Cenogenesis: kainos (Kaivos), new; genesis. 



180 AN INTRODUCTION TO ENTOMOLOGY 

Deviation from the usual type of incomplete metamorphosis. — The 

more striking deviations from the usual type of hemimetabolous devel- 
opment are the following: 

The Odonata. — In theOdonata the wings of the naiads are inverted; 
these insects resembling in this respect the Saltitorial Orthoptera. 
What is the upper surface of the wings with naiads becomes the lower 
surface in the adults, the change taking place at the last ecdysis. 

The Ephemerida. — In the Ephemerida, there exists the remarkable 
phenomenon of an ecdysis taking place after the insect has left the 
water and acquired functional wings. The winged instar that is 
interpolated between the last aquatic one and the adult is termed the 
sub-imago. 

g. COMPLETE METAMORPHOSIS 

(Holometabolus* Development) 

The representatives of several orders of insects leave the egg-shell 
in an entirely different form from that they assume when they reach 
maturity; familiar examples of these are caterpillars which develop 
into butterflies, maggots which develop into flies, and grubs which 
develop into beetles. These insects and others that when they 
emerge from the egg-shell bear almost no resemblance in form to the 
adult are said to undergo a complete metamorphosis or a holometdbolous 
development. 

The Holometabola. — Those orders that are characterized by a 
holometabolous development are grouped together as the Holometab- 
ola. This group includes the Neuroptera, Mecoptera, Trichoptera, 
Lepidoptera, Diptera, Siphonaptera, Coleoptera, and Hymenoptera. 

This grouping together of these orders, while convenient for dis- 
cussions of metamorphosis, is doubtless artificial. It is not at all 
probable that the Holometabola is a monophylitic group. In other 
words complete metamorphosis doubtless arose several times inde- 
pendently in the evolution of insects. 

The term larva. — The form in which a holometabolous insect 
leaves the egg is called larva. The term was suggested by a belief of 
the ancients that the form of the perfect insect was masked, the Latin 
word larva meaning a mask. 

Formerly the term larva was applied to the immatiu-e stages of all 
insects; but more recent writers restrict its use to the immature in- 

*Holometabolous : Jiolos {&'>^oi), complete; metabole (/ieTo^oX^), change. 



THE METAMORPHOSIS OF INSECTS 181 

stars of insects with a complete metamorphosis; and in this sense 
only is it used in this book. 

The adaptive characteristics of larvae. — The larvas of insects with 
complete metamorphosis, like the naiads of those with incomplete 
metamorphosis, exhibit an acquired form of body adapting them to 
special modes of life; and in this case the cenogenetic or "sidewise 
development" is much more marked than it is in insects with an 
incomplete metamorphosis. Here the form of the body bears but little 
relation to the form to be assumed by the adult, the nature of the 
larval life being the controlling factor. 

The differences in form between larvae and adults are augmented 
by the fact that not only have larvae been modified for special modes 
of life, but in most cases the adults have been highly specialized for a 
different mode of life; and so great are these differences that a 
quiescent pupa stage, during which certain parts of the body can be 
made over, is necessary. 

Here, as in the case of insects with an incomplete metamorphosis, we have an 
illustration of the fact that natural selection can act on any stage in the develop- 
ment of animal to better adapt that particular stage to the conditions under which 
it e-cists. Darwin pointed out in his "Origin of Species" that at whatever age 
a variation first appears in the parent it tends to reappear at a corresponding age 
in the offspring. This tendency is termed homochronous heredity* . 

It is obvious that the greater the adaptive characteristics of the immature 
forms, the less does the ontogeny of a species represent the phylogeny of the 
race to which it belongs. This fact led Fritz MuUer, in his "Facts for Darwin", 
to make the aphorism "There were perfect insects before larv£e and pupje." The 
overlooking of this principle frequently results in the drawing of unwarranted con- 
clusions, by those writers on insects who cite adaptive larval characteristics as 
being more generalized than the corresponding features of the adult. 

The more obvious of the adaptive characteristics of larvae are the 
following : 

The form of the body. — As indicated above the form of the body of a 
larva bears but httle relation to the form to be assumed by the adult, 
the nature of the larval life being the controlling factor in determining 
the form of the body. As different larvae live under widely differing 
situations, various types of lar\^as have been developed; the more 
important of these types are described later. 

The greater or less reduction of the thoracic legs. — In the evolution 
of most larvce there has taken place a greater or less reduction of the 
thoracic legs; but the extent of this reduction varies greatly. The 
larvae of certain Neuroptera, as Cory dolus for example, have as perfect 



"Homochronous: homos ipixo's), one and the same; chronos (xp^vos), time. 



182 AN INTRODUCTION TO ENTOMOLOGY 

legs as do naiads of insects with an incomplete m etamorphosis. The 
larv£e of Lepidoptera have short legs which correspond to only a part 
of the legs of the adidt. While the larvae of Diptera have no external 
indications of legs. 

The development of prolegs in some larvce. — A striking feature of 
many larvae is the presence of abdominal organs of locomotion; these 
have been termed prolegs; the prolegs of caterpillars are the most 
familiar examples of these organs. 

The prolegs were so named because they were believed to be merely adaptive 
cuticular formations and not true legs; this belief arose from the fact that they are 
shed with the last larval skin. Some recent writers, however, regard the prolegs 
as true legs. It is now known that abdominal appendages are common in the 
embryos of insects; and these writers believe that the prolegs are developed 
from these embryonic appendages, and that, therefore, they must be regarded as 
true legs. 

If this is true, there has taken place a remarkable reversal in the course ot 
development. The abdominal legs, except those that were modified into append- 
ages of the reproductive organs, the gonapophyses, were lost early in the phylogeny 
of the Hexapoda. The origin of complete metamorphosis must have taken place 
at a much later period; when, according to this belief, the abdominal appendages^ 
which had been latent for a long time, were redeveloped into functional organs. 

The development of tracheal gills. — A striking feature of many larvae 
is the possession of tracheal gills. This is obviously an adaptive 
characteristic the development of which was correlated with the 
assumption of aquatic life by forms that were primarily aerial; and 
it is also obvious that the development of tracheal gills has arisen 
indepandently many times; for they exist in widely separated families 
belonging to different orders of insects that are chiefly aerial. They 
are pDsssssed by a few lepidopterous larvas, and by the representatives 
of several families of Neuroptera, Coleoptera and Diptera. On the 
other hand, in the Trichoptera the possession of tracheal gills by the 
larvce is characteristic of nearly all members of the order. 

The internal developnent of wings. — This is perhaps the most re- 
markable of the sidewise developments of larvae. Although larvae 
exhibit no external indications of wings, it has been found that the 
rudiments of these organs arise at as early a period in insects with a 
complete metamorphosis as they do in those with an incomplete 
m.etamorphosis ; and that during lan^al life the wing rudiments attain 
an advanced stage in their development. But as these rudiments are 
invaginated there are no external indications of their presence during 
larval life. The details of the internal development of wings are dis- 
cussed later. 



THE MET A MORPHOSIS OF INSECTS 183 

Occasionally atavistic individual larvse are found which have 
external wing-buds. 

As to the causes that brought about the internal development of wings we 
can only make conjectures. It has occurred to the writer that this type of wing- 
development may have arisen as a result of boring habits, or habits of an analogous 
nature, of the stem forms from which the orders of the Holometabola sprang. 
Projecting wing-buds would interfere with the progress of a boring insect; and, 
therefore, an embedding of them in the body, thus leaving a smooth contour, 
would be advantageous. 

In support of this theory attention may be called to the fact that the larvag 
of the most generalized Lepidoptera, the Hepialidaj, are borers; the larva2 'A the 
Siricidas, which are among the more generalized of the Hymenoptera are oorers; 
so too are many Coleoptera; most larvae of Diptera are burrowers; and -he larvae 
of Trichoptera live in cases. 

The retarding of the development of the compound eyes.— One of the 
most distinctively characteristic features of larvze is the absence of 
compound eyes. The life of most larvse is such that only limited 
vision is necessary for them; and correlated with this fact is a retard- 
ing of the development of the greater portion of the compound eyes ; 
only a few separate ommatidia being functional during larval life. 

In striking contrast with this condition are the well-developed eyes 
of nymphs and naiads. 

The larvae of Corethra and Panorpa are the only larv^as known to 
me that possess compound eyes. 

The invaginated conditions of the head in the larvcB of the more 
specialized Diptera. — The extreme of sidewise development is exhib- 
ited by the larvae of the more specialized Diptera. Here not only are 
the legs and wings developed internally but also the head. This 
phenomenon is discussed later. 

The different types of larvae. — As a rule, the larvae of the insects of 
any order resemble each other in their more general characteristics, 
although they bear but little resemblance to the adult forms. Thus 
the grubs of Coleoptera, the caterpillars of Lepidoptera, or the mag- 
gots of Diptera, in most ca^es, can be recognized as such. Still in 
each of these orders there are larvse that bear almost no resemblance 
to the usual type. As examples of these may be cited the water- 
pennies (Parnidae, Coleoptera), the slug-caterpillars (Cochlidiidae, 
Lepidoptera), and the larvae of Microdon (Diptera). 

To understand the variations in form of larvae it should be borne 
in mind that the form of the body in all larvae is the result of secondary 
adaptations to peculiar modes of life; and that this modification of 
form has proceeded in different directions and in varying degrees in 
different insects. 



184 



^A^ INTRODUCTION TO ENTOMOLOGY 



Among the many types of larvs, there are a few that are of such 
common occurrence as to merit distinctive names; the more im- 
portant of these are the following: 

Campodeiform. — In many paurometabolous 
insects and in some holometabolous ones, the 
early instars resemble Campodea more or less in 
the form of the body (Fig. 202); such naiads 
and larvae are described as campodeiform. 

In this type, the body is long, more or less 
flattened, and with or without caudal setae ; the 
mandibles are well developed; and the legs are 
not greatly reduced. Among the examples of 
this type are the larvae of most Neuroptera, and 
the active larvas of many Coleoptera (Cara- 
bidas, Dysticidas, and the first instar of Me- 
loidae). 

Eruciform. — The eruciform type of larvae is 
well-illustrated by most larv« of Lepidoptera 
and of Mecoptera; it is the caterpillar form 
(Fig. 203). In this type the body is cylindrical; 
the thoracic legs are short, having only the 
terminal portions of them developed; and the 
abdomen is furnished with prolegs or with 
proleg-like cuticular folds. Although these 
larvae move freely, their powers of locomo- 
tion are much less than in the campodeiform 
type. 

Scarabeiform. — The common white grub, the larva of the May- 
beetle (Fig, 204) is the most familiar example of a scarabeiform larva. 




Fig. 202. — Campodea 
slaphylinus (After 
Lubbock). 




Fig. 203. — The silk-worm, an eruciform larva (After Verson). 



In this type the body is nearly cylindrical, but usually, especially 
when at rest, its longitudinal axis is curved ; the legs are short ; and 



THE METAMORPHOSIS OF INSECTS 



185 



prolegs are wanting. This type is quite characteristic of the lar\^£e 
of the Scarabaeidag, hence the name ; but it occurs in other groups 

of insects. 

The movements of these larvae are 

slow; most of them live in the ground, 

or in wood, or in decaying animal or 

vegetable matter. 




Vermiform. — Those larvae that are 

more or less worm-like in form are 

termed vermiform. The most striking 

features of this type are the elongated 

Fig. 204. — Larva of Melolontha form of the body and an absence of 

vukaris (After Schiodte). locomotive appendages (Fig. 205). 

Naupliiform. — The term naupliiform is applied to the first instar 

of the larva of Platygaster (Fig. 206), on account of its 

resemblance to the nauplius of certain Crustacea. 

The prepupa. — Usually the existence of an instar 
between the last lan.^al one and the pupal instar is not 
recognized. But such a form exists; and the recogni- 
tion of it becomes important when a careful study is 
made of the development of holometabolous insects. 
As is shown later, during larval life the develop- 
ment of the wings is going on within the body. As 
the larva approaches maturity, the wings reach an 
advanced stage of development within sac-like invagi- 
nations of the body-wall. Near the close of the last 
larval stadium the insect makes preparation for the 
change to the pupa state. Some form a cell within 
which the pupa state is passed, the larvae of butter- 
flies suspend themselves, and most larvae of moths spin 
a cocoon. Then follows a period of apparent rest before 
the last larv^al skm is shed and the pupal state assumed. 
But this period is far from being a quiet one; within 

the apparently motionless body important changes p^ ^^ 

take place. The most easily observed of these Larva of a 
changes is a change in the position of the wings, crane-fly. 
Each of these passes out through the mouth of the sac in which it has 
been developed, and lies outside of the newly developed pupal cuti- 
cula, but beneath the last larval cuticula. Then follows a period of 
variable duration in different insects, in which the wings are really 



186 



AN INTRODUCTION TO ENTOMOLOGY 



outside of the body although still covered by the last larval cuticula , 



this period is 




206. — 
Larva of 
Platygaster 
(After Ganin.) 



the prepupal stadium. The prepupal instar differs 
markedly from both the last larval one and from the 
pupa ; for after the shedding of the last larval cuticula 
important changes in the form of the body take place 
before the pupal instar is assimied. 

The pupa. — The most obvious characteristics of the 
pupa state are, except in a few cases, inactivity and help- 
lessness. The organs of locom.otion are functionless, 
and may even be soldered to the body throughout their 
entire length, as is usual with the pupae of Lepidoptera 
(Fig. 207). In other cases, as in the Coleoptera (Fig. 
208) and in the Hymenoptera, the wings and legs are 




free, but enclosed in more or less sac-like cuticular 
sheaths, which put them in the condition of the pro- 
verbial cat in gloves. More than this, in most cases, the legs of the 
adult are not fully formed till near the end of the pupal stadium. 

The term pupa, meaning girl, was applied to this instar by Linnseus 
on account of its resemblance to a baby that has been swathed or 
bound up, as is the custom with 
many peoples. 

Although the insect during the pupal 

stadiun^. is apparently at rest, this, from a 

physiological point of view, is the most 

active period of its postembryonic exist- 

encp; for wonderful changes in the struc- p-„ 207.— Pupa of a moth. 

cure of the body take piaffe at this time. 

In the development of a larva the primitive form of the body has been greatly 

modified to adapt it to its peculiar mode of life; tl-iis sidewise development results 
in the production of a type of body that is not at all fitted for the 
duties of adult life. In the case of an insect with incomplete meta- 
morphosis, the full grown naiad needs to be modified comparatively 
little to fit it for adult life; but the change from a maggot to a fly, 
or from a caterpiller to a butterfly, involves not merely a change 
in external form but a greater or less remodeling of its entire 
structure. These changes take place during the period of apparent 
. est, the prepupal and pupal stadia. 

The chrymlis.— The term chrysalis is often applied to 

the pupffi of butterflies. It was suggested by the golden ^ 

spots with which the pups of certain butterflies are 

ornamented. 

Two forms of this word are in use: first, chrysalis, the plural of 

which is chrysalides; and second, chrysalid, the pltiral of which is 




THE METAMORPHOSIS OF INSECTS 



187 



chrysalids. The singular of the first form and the plural of the second 
are those most often used. 

Active piipcB. — The pupae of mosquitoes and of certain midges are 
remarkable for being active. Although the wings and legs are func- 
tionless, as with other pupae, these creatures are able to swim by 
means of movements of the caudal end of the body. 

In several genera of the Neuroptera (Chrysopa, Hemerobius, and 
Raphidia) the pupa becomes active and crawls about just before 
transforming to the adult state. 

Movements of a less striking character are made by many pups, 
which work their way out of the ground, or from burrows in wood, 
before transforming. In some cases, as in the pup« of the carpenter- 
moths (Cossidce) the pupa is armed with rows of backward projecting 
teeth on the abdominal segments, which facilitate the movements 
within the burrow. 

The creniaster. — Many pupae, and especially those of most Lepidop- 
tera, are provided with a variously shaped process of the posterior 
end of the body, to which the term creniaster is applied. This process 
is often provided with hooks which serve to suspend the pupa, as in 
butterflies, or to hold it in place, after it has partly emerged from the 
cocoon, and while the adult is emerging from the pupal skin, as in 
cocoon-making moths. In its more simple form, where hooks are 
lacking, it aids the pupa in working its way out of the earth, or from 
other closed situations. 

The method of fixing the cremaster in the disk of silk from which 
the pupa of a butterfly is suspended was well-illustrated by C. V. Riley 
('79). The full grown larva spins this disk and hangs from it during 

the prepupal stadium 
by means of its anal 
prolegs (Fig. 209, a). 
When the last larval 
skin is shed, it is 
worked back to the 
caudal end of the body 
(Fig. 209, b); and is 
then grasped between 
two of the abdominal 
segments (Fig. 209, c,) 
while the caudal end of the body is removed from it ; and thus the 
cremaster is freed, and is in a position from which it can be inserted 
in the disk of silk. 




Fig. 209. — Transformations of the milkweed butter- 
fly (From Riley). 



188 AN INTRODUCTION TO ENTOMOLOGY 

The cocoon. — The pupal instar is an especially vulnerable one. 
During the pupal life the insect has no means of offence, and having 
exceedingly limited powers of motion, it has almost no means of 
defense unless an armor has been provided. 

Many larvae merely retreat to some secluded place in which the 
pupal stadium is passed ; others bury themselves in the ground ; and 
still others make provision for this helpless period by spinning a silken 
armor about their bodies. Such an armor is termed a cocoon. 

The cocoon is made by the full-grown larva; and this usually 
takes place only a short time before the beginning of the pupal stadium. 
But in some cases several months elapse between the spinning of the 
cocoon and the change to pupa, the cocoon being made in the autimm 
and the change to pupa taking place in the spring. Of course a 
greater or less portion of this period is occupied by the prepupal 
stadium. 

Cocoons are usually made of silk, which is spun from glands 
already described. In some cases, as in the cocoons of Bomhyx, the 
silk can be unwound and utilized by man. 

While silk is the chief material used in the making of cocoons, it is 
by no means the only material. Many wood-boring 
larvas make cocoons largely of chips. Many insects that 
undergo their transformation in the ground incorporate 
earth in the walls of their cocoons. And hairy cater- 
pillars use silk merely as a warp to hold together a 
woof of hair, the hairs of the larva being the most con- 
spicuous element in the cocoon. 

In those cases in which silk alone is used there is a 
great variation in the nature of the silk, and in the den- 
sity of the cocoon. The well-known cocoons of the 
saturniids illustrate one extreme in density, the cocoons 
of certain Hymenoptera, the other. 

The fiberous nature of the cocoon is usually obvious ; 

but the cocoons of saw-flies appear parchment -like, and 

Fig. 2IO.— the cocoons of the sphecids appear like a delicate foil. 

cocoon^ of While in the more common tjrpe of cocoons the 

Trichostibas wall is a closely woven sheet, there are cocoons that 

from ^ which ^^^ lace-like in texture (Fig. 210). 

the adult has Modes of escape from the cocoon. — The insect, having 

^^ ■ walled itself in with a firm layer of silk, is forced to meet 

the problem of a means of escape from this inclosure; a problem 

which is solved in greatly varied ways. 




THE METAMORPHOSIS OF INSECTS 



189 



In many insects in which the adult has biting mouth parts, the 
adult merely gnaws its way out by means of its mandibles In some 
cases, as the Cynipidce, it is said that this is the only use made of 
its mandibles by the adult. 

In some cases the mandibles with which the cocoon is pierced per- 
tain to the pupal instar, this is true of Chrysopa and Hemerobius; 
and the Trichoptera break out from their cases, by means of their 
mandibles, while yet in the pupal state. 

For those insects in which the adult has sucking mouth parts, the 
problem is even more difficult. Here it has been met in several quite 
distinct ways. The pupse of many Lepidop- 
tera possess a specialized organ for breaking 
through the cocoon; in some the anterior 
end of the pupa is furnished with a toothed 
crest (LithocoUetes hamadryella) ; in certain satur- 
niids there is a pair of large, stout, black spines, 
one on each side 
of the thorax, at 
the base of the 
fore wings with 
which the adult 
cuts a sHt in the 
cocoon through 

which the moth emerges, this was obser\'ed by 
Packard in Tropcea luna; but as these spines are 
present in other saturniids, where the cocoon is too 
. ^._ ,^i. dense to be cut by them, and where an opening is 
h^^i^mil made in some other way, 
it is probable that, as a 
rule, their function is loco- 
motive, aiding the.moth to 
work its way out from the 
cocoon, by a wriggling 
motion. 

One of the ways in 
which saturniids pierce 

their cocoons is that practiced by Bombyx and Telea. 
These insects soften one end of the cocoon by a 
liquid, which issues from the mouth; and then, by- 
forcing the threads apart or by breaking them, make an opening. 





Cocoon of Megalopyge oper- 



Fig. 211. — Longi- 
tudinal section 
of a cocoon of 
Callosamia pro- 
melhea;v, valve- 
like arrange- 
ment for the 
escape of the 
adult. 




Fig. 213. — Old cocoon of 
Megalopyge opercularis. 



190 AN INTRODUCTION TO ENTOMOLOGY 

Far more wonderful than any of the methods of emergence from 
the cocoon described above are those in which the larva makes pro- 
vision for the escape of the adult. The most familiar of these is that 
practiced by the larv^as of Samia cecropia and Callosamia promethea. 
These larvae when they spin their cocoons construct at one end a coni- 
cal valve-like arrangement, which allows the adult to emerge without 
the necessity of making a hole through the cocoon (Fig. 211, v). A 
less familiar example, but one that is fully as wonderful, is that of 
a Megalopyge. The larva of this species makes a cocoon of the 
form shown in Figure 212. After an outer layer of the cocoon has 
been made, the larva constructs, near one end of it, a hinged partition ; 
this serves as a trap door, through which the moth emerges. That 
part of the cocoon that is outside of the partition is quite delicate and 
is easily destroyed. Hence most specimens of the cocoons in col- 
lections present the appearance represented in Figure 213. 

The puparium. — The pupal stadiimi of most Diptera is passed 
within the last larval skin, which is not broken till the adult fly is 
ready to emerge. In this case the larval skin, which becomes hard 
and brown, and which serves as a cocoon, is termed a 
puparium. In some families the puparium retains the 
form of the larva; in others the body of the larva 
shortens, assuming a more or less barrel-shaped form, 
before the change to a pupa takes place (Fig. 214). 

Modes of escape from the puparium. — The pupse of 
the more generalized Diptera escape from the pupa- 
rium through a T-shaped opening, which is formed by 
a lengthwise split on the back near the head end and a 
crosswise split at the front end of this (Fig. 215), or 
rarely, through a cross-wise split between the seventh 
-Pupa- and eighth abdominal segments. In the more special- 
■'^''^''ized Diptera there is developed a large bladder-like 
organ, which is pushed out from the front of the head, 
through what is known as the frontal suture, and by which the head 
end of the puparium is forced off. This organ is known as the ptilinum. 
After the adult escapes, the ptilinum is withdrawn into the head. 

The Different types of pupaB. — Three types 
of pupce are commonly recognized; these 
are the following: Fig. 215.— Puparium of a 

Exarate pupcB. — Pupae which, like those ^ ''^ lomyu 
of the Coleoptera and Hymenoptera, have the legs and. vnngs free, 
are termed exarate pupag. 




THE METAMORPHOSIS OF INSECTS 191 

Oocected pupce. — Pups which like the pupse of Lepidoptera, have 
the limbs glued to the surface of the body, are termed obtected pupas. 

Coarctate Pupce. — Pupas that are enclosed within the hardened 
larval skin, as is the case with the pupae of most of the Diptera, are 
termed coarctate pupae. 

The imago — The fully developed or adult insect is termed the 
imago. 

The life of the imago is devoted to making provision for the 
perpetuation of the species. It is during the imaginal stadium that 
the sexes pair, and the females lay their eggs. With many species 
this is done very soon after the last ecdysis ; but with others the egg- 
laying is continued over a long period; this is especially true with 
females of the social Hymenoptera. 

h. HYPERMETAMORPHOSIS 

There are certain insects, representatives of several different orders 
that exhibit the remarkable peculiarity in their development that the 
successive larval instars represent different types of larvae. Such 
insects are said to undergo a hypermetamorphosis. 

The transformations of several of these insects will be described 
later in the accounts of the families to which they belong; and for 
this reason, in order to avoid repetition, are not discussed here. The 
more striking examples are Mantispa, Meloe, Stylops, and Platy- 
gaster. 

i. VIVIPAROUS INSECTS 

There are many insects that produce either nymphs or larvae 
instead of laying eggs. Such insects are termed viviparous. This 
term is opposed to oviparous, which is applied to those insects that lay 
eggs that hatch after exclusion from the body. 

It has been pointed out in the discussion of the reproductive organs that, from 
the primordial germ -cells, there are developed in one sex spermatoza and in the 
other eggs; and it should be borne in mind that the germ-cells produced in the 
ovary of a female from the primordial germ-cells are eggs. These eggs grow and 
mature; in some cases they become covered with a shell, in others they are not 
so covered; in some cases they are fertilized by the union of a spermatozoan with 
them, and in others they are never fertilized; but in all these cases they are eggs. 
We may say, therefore, that all insects are developed from eggs. 

A failure to recognize this fact has introduced confusion into entomological 
literature. Some writers have termed the germ-cells produced by agamic aphids 
pseudova or false eggs. But these germ-cells are as truly eggs as are those from 
which the males of the honeybee develop; they are merely unfertilized eggs. 
The term pseudovum conveys a false impression; while the phrase, an unfer- 
tilized egg, clearly states a fact. 



192 AN INTRODUCTION TO ENTOMOLOGY 

Some writers make use of the term ovoviviparous indicating the production 
of eggs that have a well -developed shell or covering, but whicK hatch within the 
body of the parent; but the distinction is not fundamental, since viviparous ani- 
mals also produce eggs as indicated above. 

Among viviparous insects there are found every gradation from 
those in which the larvse are born when very young to those in which 
the entire larval life is passed within the body of the parent. There 
also exist examples of viviparous larvae, viviparous pupae, and vivi- 
parous adults. And still another distinction can be made; in some 
viviparous insects the reproduction is parthenogenetic ; in others it 
is sexual. 

Viviparity with parthenogenetic reproduction. — In certain vivipar- 
ous insects the reproduction is parthenogenetic ; that is, the young are 
produced from eggs that are not fertilized. This type of reproduction 
occurs in larvae, pupas, and apparently in adults. 

Pcsdogenetic Larvae. — In 1862 Nicholas Wagner made the remark- 
able discovery that certain larvae belonging to the Cecidomyiidae give 
birth to living young. This discovery has been confirmed by other 
observers, and for this type of reproduction the term pcsdogenesis, 
proposed by Von Baer, has come into general use. This term is also 
spelled pedogenesis; the word is from pcedo or pedo, a child, and genesis. 

The phenomenon of paedogenesis is discussed later in the accounts 
of the Cecidomyiidae and of the Micromalthidas. 

Pcedogenetic pupce. — The most frequently observed examples of 
paedogenetic reproduction are by larv^ae ; but that pupae also are some- 
times capable of reproduction is shown by the fact that Grimm ('70) 
found that eggs laid by a pupa of Chironomus grimrni, and of coxu"se 
not fertilized, hatched. 

Anton Schneider ('85) found that the adults of this same species of 
Chironomus reproduced parthenogenetically. This species, therefore, 
exhibits a transition from pedogenesis to normal parthenogenesis. 

Viviparous adult agamic females. — There may be classed under this 
class provisionally, the agamic females of the Aphididae; as these are 
commonly regarded as adults. It has been suggested, however, that 
the agamic reproduction of the Aphids may be a kind of pasdogenesis ; 
the agamic females being looked upon as nymphs. This however, is 
not so evident in the case of the winged agamic generation. On the 
other hand, the reproductive organs of the agamic aphids are incom- 
pletely developed, as compared with those of the sexual forms, lacking 
a spermatheca and colleterial glands. 



THE MET A MORPHOSIS OF INSECTS 193 

This discussion illustrates the difficulty of attempting to make sharp distinc- 
tions, whereas in nature all gradations exist between different types of structure 
and of development. Thus Leydig ('67) found a certain aphid to be both ovipar- 
ous and viviparous; the eggs and the individuals born as nymphs being produced 
from neighboring tubes of the same ovary. 

Viviparity with sexual reproduction. — Although most insects that 
reproduce sexually are oviparous, there are a considerable number in 
which sexual reproduction is associated with viviparity. 

Among these sexual viviparous insects there exist great differences 
in method of reproduction ; with some the young are born in a very 
immature stage of development, a stage corresponding to that in 
which the young of oviparous insects emerge from the egg; while 
with others the young attain an advanced stage of development 
within the body of the mother. 

Sexual viviparous insects giving birth to nymphs or larvce. — That 
type of viviparity in which sexual females give birth to very immature 
nymphs or larvae exists in more or less isolated members of widely 
separated groups of insects. As the assumption of this type of repro- 
duction involves no change in the structure of the parent, but merely 
a precocious hatching of the egg, it is not strange that it has arisen 
sporadically and many times. In some cases, however, the change is 
not so slight as the foregoing statement would imply; as, for example, 
in the case of the viviparous cockroach, which does not secrete 
oothecae as do other cockroaches. 

Among the recorded examples of this type of viviparity are 
representatives of the Ephemerida, Orthoptera, Hemiptera, Lepi- 
doptera, Coleoptera, Strepsiptera, and Diptera. 

Sexual viviparous insects giving birth to old larvce. — The mode of 
reproduction exhibited by these insects is doubtless the most excep- 
tional that occurs in the Hexapoda, involving, as it does, very impor- 
tant changes in the structure of the reproductive organs of the fe- 
males. 

With these insects the larvae reach maturity within the body of the 
parent, undergoing what is analogous to an intra-uterine develop- 
ment, and are born as full-grown larvae. This involves the secretion 
of a "milk" for the nourishment of the young. 

This mode of reproduction is characteristic of a group of flies, 
including several families, and known as the Pupipara. This name 
was suggested for this group by the old belief that the young are born 
as pupas ; but it has been found that the change to pupa does not take 
place till after the birth of the larva. 



194 AN INTROD UCTION TO ENTOMOLOG Y 

The reproduction of the sheep-tick, Melophagns oviniis, may be 
taken as an illustration of this type of development ; this is described 
in the discussion of the Hippoboscidse, the family to which this insect 
belongs. 

The giving birth to old larvce is not restricted to the Pupipara. 
Surgeon Bruce (quoted by Sharp, 'gg) has shown that the Tsetse fly, 
Glossina morsitans, reproduces in this way, the young changing to 
pupee immediately after birth. 

An intermediate type of development is illustrated by Hylemyia 
strigosa, a dung-frequenting fly belonging to the Anthomyiidse. 
This insect, according to Sharp ('99), produces living larvee, one at a 
time. "These larvae are so large that it would be supposed they are 
full-grown, but this is not the case, they are really only in the first 
stage, an unusual amount of growth being accomplished in this 
stadium." 

j. NEOTEINIA 

The persistence with adult animals of larval characteristics has 
been termed neoteinia* or neotenia. When this term first came into 
use it was applied to certain amphibians, as the axolotle, which retains 
its gills after becoming sexually mature; but it is now used also in 
entomology. 

The most familiar examples of neoteinic insects are the glow- 
worms, which are the adult females of certain beetles, the complemen- 
tal females of Termites, and the females of the Strepsiptera. 



II. THE DEVELOPMENT OF APPENDAGES 

In the preceding pages the more obvious of the changes in the 
external form of the body during the metamorphosis of insects and 
some deviations from the more common types of development have 
been discussed. The changes in the form of the trunk that have been 
described are those that can be seen without dissection; but it is 
impracticable to limit a discussion of the development of the appen- 
dages of the body in this way, for in the more specialized types of 
metamorphosis a considerable part of the development of the appen- 
dages takes place within the body -wall. 



•^Neoteinia: neos (v^os), youthful; teinein {rebeiv), to stretch. 



THE METAMORPHOSIS OF INSECTS 195 

a. THE DEVELOPMENT OP WINGS 

Two quite distinct methods of development of wings exist in 
msects; by one method, the wings are developed as outward project- 
ing appendages of the body; by the other, they reach an advanced 
stage of development within the body. The former method of 
development takes place with nymphs and naiads, the latter with 
larvct* 

I. The Development oj the Wings of Nymphs and Naiads 

In insects with a gradual or with an incomplete metamorphosis the 
development of the appendages proceeds in a direct manner. The 
wings of nymphs and naiads are sac-like outgrowths of the body-wall, 
which appear comparatively early in life and become larger and larger 
with successive molts, the expanding of the wing-buds taking place 
immediately after the molt ; an illustration of this has been given in 
the discussion of gradual metamorphosis, page 175. 

2. Development of the Wings in Insects vuith a Complete 
Metamorphosis 

Although there are differences in details in the development of the 
wings in the different insects undergoing a complete metamorphosis, 
the essential features are the same in all. The most striking feature 
is that the rudiments of the wings, the wing-buds, arise within the 
body and become exposed for the first time when the last larval skin 
is shed. The development of the wings of the cabbage butterfly 
{Pontia rapce) will serve as an example of this type of development of 
wings. The tracing of that part of this development which takes 
place during the larval life can be obsen^ed by making sections of the 
body-wall of the wing-bearing segments of the successive instars of 
this insect. 

The fiisc indication of a wing-bud is a thickening of the hypo- 
dermis; this thickening, known as a histoblast or an imaginal disc, 
has been observed in the embryos of certain insects, in the first 
larval instar of the cabbage butterfly it is quite prominent (Fig. 
216, a). During the second stadium, it becomes more prominent 
and is invaginated, forming a pocket-like structure (Fig. 216, 6). 
During the third stadium a part of this invagination becomes 
thickened and evaginated into the pocket formed by the thinner 



*Only the more general features of the development of wings are discussed 
here. For a fuUer account see "The Wings of Insects" (Comstock '18, a). 



196 



AN INTRODUCTION TO ENTOMOLOGY 



portions of tne invagination (Fig. 216, c). During the fourth 
stadium, the evaginated part of the histoblast becomes greatly- 
extended (Fig. 216, d). 
It is this evaginated 
portion of the histo- 
blast that later be- 
comes the wing. Dur- 
ing the fifth stadium 
the wing-bud attains 
the form shown in 
Figure 216, e, which 
represents it dissected 
out of the wing-pocket 
At the close of the last 
larval stadium, the 
fifth , the wing is pushed 
out from the wing-poc- 
ket, and Hes under the 
old larval cuticula dur- 
ing the prepupal sta- 
dium. It is then of 
the form shown in 
Figure 216, /. The 
molt that marks the 
beginning of the pupal 
stadium, exposes the 
wing-buds, which in 
the Lepidoptera be- 
come closely soldered 
to the sides and breast 
of the pupa. Imme- 
diately after the last 
molt when the adult 
emerges, the wings 
Fig. 216.— Several stages in the development of the expand greatly and 
wings of a cabbage butterfly (After Mercer). assume their definitive 

form. 

While this increase in size and changes in form of the developing 

wing are taking place, there occur other remarkable developments in 

its structure. A connection is made with a large trachea near which 

the histoblast is developed, shown in cross-section in the first four 




THE METAMORPHOSIS OF INSECTS 197 

parts (a, b, c, and d) of Figure 216; temporary respiratoiy organs, 
consisting of bundles of tracheoles, are developed (e and/) ; and later, 
near the close of the larval period, the trachese of the wing are devel- 
oped, and the bundles of tracheoles disappear. During the later 
stages in the development of the wing the basement membranes of the 
hypodermis of the upper and lower sides of the wing come together, 
except along the lines where the veins are to be developed later, and 
become united. In this way the wing is transformed from a bag-like 
organ to a sheet-like one. The hnes along which the two sides of the 
wing remain separate are the vein cavities ; in these the trunks of the 
wing-tracheag extend. During the final stages of the development of 
the wing, the walls of the vein-cavities are thickened, thus the wing- 
veins are formed; and the spaces between the wing-veins become thin. 

By reference to Figure 216, c and d, it will be seen that the histo- 
blast consists of two quite distinct parts, a greatly thickened portion 
which is the wing-bud and a thinner portion which connects the wing- 
bud with the hypodermis of the body-wall, and which constitutes the 
neck of the sac-like histoblast, this is termed the peripodal membrane, 
a term suggested by the similar part of the histoblast of a leg ; and the 
enclosed cavity is known as the peripodal cavity. 

In the more specialized Diptera, the peripodal membranes are 
very long and both the wing-buds and the leg-buds are far removed 
from the body-wall. A condition intermediate between that which 
exists in the Lepidoptera, as shown in Figure 216, and that of the 
more speciaHzed Diptera was found by Kellogg (07) in the larva of 
Holorusia rubiginosa, one of the 
crane-flies (Fig. 217). 

b. THE DEVELOPMENT OF LEGS 

The development of the legs 
pi oceeds in widely different ways 

in different insects. In the ^. „,. , , . , , ^ ,, 

,. , . , Fig. 217. — Wing- bud m the larva of the 

more generalized forms, the giant crane-fly, Holorusia rubiginosa; 
legs of the embryo reach an ^3-, hypodermis; pm peripodal mem- 
brane; /, trachea; wo, wmg-bud (Alter 
advanced stage of development Kellogg). 

before the nymph or naiad 

leaves the egg-shell, and are functional when the insect is born; on 
the other hand, in those specialized insects that have vermiform larvas, 
the development of the legs is retarded, and these organs do not 
become functional until the adult stage is reached. Almost every 
conceivable intergrade between these two extremes exist. 




198 AN INTRODUCTION TO ENTOMOLOGY 

I. The Development of the Legs of Nymphs and of Naiads 

In insects with a gradual metamorphosis and also in those with an 
incomplete metamorphosis the nymph or naiad when it emerges from 
the eggshell has well-developed legs, which resemble quite closely 
those of the adult. The changes that take place in the form of the 
legs during the postembyronic development are comparatively slight ; 
there may be changes in the relative sizes of the different parts ; and 
in some cases there is an increase in the number of the segments of the 
tarsus ; but the changes are not sufficiently great to require a descrip- 
tion of them here. 

2. The Development of the Legs in Insects with a Complete Metamor- 
phosis 

It is a characteristic of most larvse that the development of their 
legs is retarded to a greater or less extent. This retardation is least 
in campodeiform larvae, more marked in cruciform larv^, and reaches 
its extreme in vermiform larvee. 

The development of the legs of insects with campodeiform larvae. — 

Among the larvae classed as campodeiform the legs are more or less 
like those of the adults of the same species ; there may be differences 
in the proportions of the different segments of the leg, in the number 
of the tarsal segments, and in the number and form of the tarsal claws ; 
but these differences are not of a nature to warrant a discussion of 
them here. These larvs lead an active life, like that of nymphs, 
and consequently the form of legs has not been greatly modified from 
the paurometabolous type. 

The development of the legs of insects with erucif orm larvae. — In 

caterpillars and other cruciform larvee the thoracic legs are short and 
fitted for creeping ; this mode of locomotion being best suited to their 
mode of life, either in burrows or clinging to foliage. This form of leg 
is evidently an acquired one being, like the internal development of 
wings, the result of those adaptive changes that fit these XsltvcQ to lead 
a very different life from that of the adults. 

In the case of caterpillars the thoracic legs are short, they taper 
greatly, and each consists of only three segments. It has been com- 
monly believed and often stated that the three segments of the larval 
leg correspond to the terminal portion of the adult leg ; but studies of 
the development of the legs of adults have shown that the divisions 
of the larval leg have no relation to the five divisions of the adult leg. 



THB METAMORPHOSIS OF INSECTS 199 

It has been shown by Gonin ('92), Kellogg ('01 and '04), and 
Verson (04) that histoblasts which are the rudiments of the legs of the 
adult exist within the body-wall of the caterpillar at the base of the 
larval legs. Late in the larval life the extremity of the legs of the 
adult are contained in the legs of the caterpillar. It has been shown 
that the cutting off of a leg of a caterpillar at this time results in a 
mutilation of the terminal part of the leg of the adult. 

The development of the legs of the adult within the body of cater- 
pillars has not been studied as thoroughly as has been the develop- 
ment of the wings ; but enough is known to show that in some respects 
the two are quite similar; this is especially true of the development of 
the tracheoles and of the tracheas. 

The development of the legs in insects with vermiform larvae. — In 
vermiform larvae the development of the entire leg is retarded. The 
leg arises as a histoblast, which is within the body and bears, in its 
more general features, a resemblance to the wing-buds of the same 
insect. The development of the legs of vermiform larvae has been 
studied most carefully in the larvse of Diptera. During the larval 
life the leg becomes quite fully developed within the peripodal cavity; 
in Corethra, they are spirally coiled; in Musca, the different segments 
telescope into each other. At the close of the larval period, the 
evagination of the legs takes place. 

C. THE DEVELOPMENT OF ANTENNA 

I. The Transformation of the Antennaz of Nymphs and of Naiads 
In the case of n3Tiiphs and of naiads the insect when it emerges 
from the eggshell has well-developed antennee. The changes that 
take place during the postembryonic development are, as a rule, com- 
paratively slight; in most insects, an increase in the number of the 
segments of the antennse takes place ; but in the Ephemerida, a reduc- 
tion in number of the antennal segments occurs. 

2. The Development of the Antennce in Insects with a Complete 
Metamorphosis 

One of the marked characteristics of larvae is the reduced condition 
of the antennse; even in the campodeiform larvas of the Neuroptera, 
where the legs are comparatively w^ell-developed, the antennae are 
greatly reduced. 

In cruciform larvae the development of the antennas follows a 
course quite similar to that of the legs. The larval antennas are small: 




200 AN INTRODUCTION TO ENTOMOLOGY 

the antennae of the adult are developed from histoblasts within the 
head and during the latter part of the larval life are folded like the 

bellows of a closed accor- 
dian; at the close of this 
period they become eva- 
ginated, but the definitive 
form is not assumed until 
the emergence of the adult. 
A similar course of devel- 
/ m^ opment of the antennae 
takes place in vermiform 
larvae (Fig. 218). 

d. THE DEVELOPMENT OF 

Fig. 218. — .Sagittal section through headof old THE MOUTH-PARTS 
lan^a of 5/;«u/^'mw, showing forming imaginal 

head paits within. Ic, larval cuticula; id. Great differences exist 

imagi-al head-wall; la, larval antenna; ia, among insects with refer- 

imagmal antenna; ie, imagmal eye; Imd, ° 

larval mandible; imd, imaginal mandible; ence tO the comparative 

h:x larval maxilla; imx, imaginal maxilla; structure of their mouth- 
Ih, larval labmm; tit, imagmal labium (rrom 

Kellogg). parts in their immature 

and adult instars. In 
some insects the immature instars have essentially the same type of 
mouth-parts as the adults ; in most of these cases, the mouth-parts are 
of the biting types, but in the Homoptera and Heteroptera both 
nymphs and adults have them fitted for sucking; in many other 
insects, the mouth-parts of the larvae are fitted for biting while those of 
adults are fitted for sucking; and in still others, as certain maggots, the 
development of the mouth-parts is so retarded that they are first 
functional in the adult insect. Correlated with these differences are 
differences in the method of development of these organs. 

In those insects that have a gradual or incomplete metamorphosis 
and in the Neuroptera, the Coleoptera, and the Hymenoptera in part, 
the mouth-parts of the immature and adult instars are essentially of 
the same type. In these insects the mouth-parts of each instar are 
developed within the corresponding mouth-parts of the preceding 
instar. At each ecdysis there is a molting of the old cuticula, a 
stretching of the new one before it is hardened, a result of the growth 
in size of the appendages, and sometimes an increase in the number 
of the segments of the appendage. In a word, the mouth-parts of the 
adult are developed from those of the immature instar in a compara- 
tively direct manner. In some cases, however, where the mouth- 



THE METAMORPHOSIS OF INSECTS 201 

parts of the larva are small and those of the adult are large, only the 
tips of the developing adult organs are within those of the larva at the 
close of the larval period, a considerable part of the adult organs being 
embedded in the head of the old larva. 

In a few Coleoptera and Neuroptera (the Dytiscidas, Myrme- 
leonidae, and Hemerobiidas) the larvae, although mandibulate, have 
the mouth-parts fitted for sucking. In these cases the form of the 
mouth-parts have been modified to fit them for a peculiar method of 
taking nourishment during the larval life. The mouth-parts of the 
adults are of the form characteristic of the orders to which these 
insects belong. 

In those insects in which the larvag have biting mouth-parts and 
the adults those fitted for sucking, the development is less direct. In 
the Lepidoptera, for example, to take an extreme case, there are great 
differences in the developmeoc oi the different organs; within the 
mandibles of the old larvae there are no developing mandibles, these 
organs being atrophied in the adult; but at the base of each larval 
maxilla, there is a very large, invaginated histoblast, the developing 
maxilla of the adult; these histoblasts become evaginated at the 
close of the larval period, but the maxillae do not assimie their defini- 
tive form till after the last ecdysis. 

The extreme modification of the more usual course of development 
of the mouth-parts is found in the footless and headless larvae of the 
more specialized Diptera. Here the mouth-parts do not appear 
externally until during the pupal stadium and become functional only 
when the adult condition is reached. See the figures illustrating the 
development of the head in the Muscidas (Fig. 220). 

It should be noted that the oral hooks possessed by the larvae of the 
more specialized Diptera are secondarily developed organs and not 
mouth-parts in the sense in which this term is commonly used. These 
oral hooks serve as organs of fixation in the larv^as of the CEstridae and 
as rasping organs in other larvas. 



e. THE DEVELOPMENT OF THE GENITAL APPENDAGES 

The development of the genital appendages of insects has been 
studied comparatively little and the results obtained by the different 
investigators are not entirely in accord ; it is too early therefore to do 
more than to make a few general statements. 

In the nymphs of insects with a gradual metamorphosis rudimen- 
tary genital appendages are more or less prominent and their develop- 



202 AN INTRODUCTION TO ENTOMOLOGY 

ment follows a course quite similar to that of the other appendages of 
the body. 

In insects with a complete metamorphosis the genital appendages 
are represented in the larv« by invaginated histoblasts; the develop- 
ing appendages become evaginated in the transformation to the pupa 
state and asstime their definitive form after the last ecdysis. 

III. THE DEVELOPMENT OF THE HEAD IN THE 
MUSCID^ 

In the more generalized Diptera the head of the larva becomes, 
with more or less change, the head of the adult ; the more important 
of these changes pertain to the perfecting of the organs of sight and the 
development of the appendages, the antennse and mouth-parts. 

But in the more specialized Diptera there is an anomalous retard- 
ing of the development of the head, which is so great that the larvae 
of these insects are commonly referred to as being acephalous. This 
retarded development of the head has been carefully studied by Weis- 
man ('64), Van Rees ('88) and Kowalevsky ('87). The accompanying 
diagrams (Fig. 220) based on those given by the last two authors illus- 
trate the development of the head in Musca, which will serve as an 
illustration of this type of development of the head. 

The larvas of Musca 
are conical (Fig. 219); and 
the head-region is repre- 
sented externally only by 
the minute apical segment 
Fig.2l9.— Larva of the house-fly, If M5ca of the conical body. It 
do we5/tca (After Hewitt). .„ , , , ,1 . 

Will be shown later that 

this segment is the neck of the insect, the developing head being 
invaginated within this and the following segments. This invagina- 
tion of the head takes place during the later embryonic stages. 

In Figure 220 are given diagrams, adapted from Kowalevsky and 
Van Rees. representing three stages in the development of the head of 
Musca. Diagram A represents the cephaHc end of the body of a 
larva; and diagram B and C, the corresponding region in a young and 
in an old pupa respectively; the parts are lettered uniformly in the 
three diagrams. 

The three thoracic segments (1,2, and 3) can be identified by the 
rudiments of the legs (/^ /-, and P). In the larva (A) the leg-buds 
are far within the body, the peripodal membrane being connected with 




THE METAMORPHOSIS OF INSECTS 



203 



the hypodermis of the body-wall by a slender stalk-like portion. In 
the young pupa (B) the pcripodal membranes of the histoblasts of the 
legs are greatly shortened and the leg-buds are near the surface of the 
body; and in the old pupa (C) the leg -buds are evaginated. The 
wing-buds are omitted in all of the diagrams. 

In the first two segments of the body of the larva (A) there is a 
cavity (ph) which has been termed the "pharynx" ; this is the part in 
which the oral hooks characteristic of the larvas of the Muscidas 
develop. The name pharynx is unfortunate as this is not a part of the 
alimentary canal; it is an invaginated section of the head, into the 
base of which the oesophagus (a) now opens. 

In the figure of the lar\^a (A) note the following parts: the 
oesophagus (cb) ; the ventral chain of ganglia (vg), the brain (b), and a 




Fig. 220. — Development of the head in the Muscidae. A, larva; B, youn^ pupa ; 
C, old pupa (From Korschelt and Heider after Kowalevsky and Van Rees). 

sac (ba) extending from the so-called pharynx to the brain. There are 
two of these sacs, one applied to each half of the brain, but only one of 
these would appear in such a section as is represented by the diagram. 
These sacs were termed the brain-appendages by Weismann. In each 
of the "brain-appendages" there is a disc-like thickening near the 
brain, the optic disc (od) ; this is a histoblast which develops into a 
compound eye ; in front of the optic disc there is another prominent 
histoblast ; the frontal disc (fd), upon which the rudiment of an antenna 
(at) is developed. 

In the larA^a the brain and a considerable part of the "brain- 
appendages" lie within the third thoracic segment. In the young 
pupa (B) these parts have moved forward a considerable distance; 
and in the old pupa (C) the head has become completely evaginated. 
The part marked p in the two diagrams of the pupa is the rudiment 
of the proboscis. 



204 AN INTRODUCTION TO ENTOMOLOGY 

By comparing diagrams B and C it will be seen that what was the 
tip of the first segment of the larva and of the young pupa (++) 
becomes the neck of the insect after the head is evaginated. 

IV. THE TRANSFORMATIONS OF THE INTERNAL 
ORGANS 

Great as are the changes in the external form of the body during 
the life of insects with a complete metamorphosis, even greater changes 
take place in the internal organs of some of them. 

In the space that can be devoted to this subject in this work, only 
the more general features of the transformation of the internal organs 
can be discussed; there is an extensive and constantly increasing 
literature on this subject which is available for those who wish to study 
it more thoroughly. 

In insects with a gradual or with an incomplete metamorphosis 
there is a continuous transformation of the internal organs, the changes 
in form taking place gradually : being quite comparable to the gradual 
de velopment of the external organs ; but in insects with a complete 
metamorphosis, where the manner of life of the larva and the adult 
are very different, extensive changes take place during the pupal 
stadium. The life of a butterfly, for example, is very different from 
that it led as a caterpillar; the organs of the larva are not fitted to 
perform the functions of the adult ; there is consequently a necessity 
for the reconstruction of certain of them; hence the need of a pupal 
stadium. Pupae are of ten referred to as being quiet ; but physiologi- 
cally the pupal period is the most active one in the post-embryonic 
life of the insect. 

In those cases where a very marked change takes place in the 
structure of internal organs, there is a degeneration and dissolution of 
tissue, this breaking down of tissues is termed histolysis- 

In the course of histolysis some cells, whicii are irequentiy leu- 
cocytes or white blood corpuscles, feed upon the debris of the disin- 
tegrating tissue ; such a cell is termed a phagocyte, and the process :1s 
termed phagocytosis. It is believed that the products of the digestion 
of disintegrating tissue by the phagocytes pass by diffusion into the 
surrounding blood and serve to nourish new tissue. 

After an organ has been raore or less broken down by histolysis, 
the extent of the disintegration differing greatly :r different organs 
and in different insects, ther3 follows a growth ci new tissue; this 
process is termed histogenesis. 



THE MET A MORPHOSIS OF INSECTS 205 

The histogenetic reproduction of a tissue begins in the differentia- 
tion and multiplication of small groups of cells, which were not 
affected by the histolysis of the old tissue; such a group of cells is 
termed an imaginal disc or a Mstoblast. They were termed imaginal 
discs on account of the disc-like form of those that were first described 
and because they are rudiments of organs that do not become func- 
tional till the imago stage ; but the term histoblast is of more general 
application and is to be preferred. 

The extent of the transformation of the internal organs differs 
greatly in dift'erent insects. In the Coleoptera, the Lepidoptera, the 
Hymenoptera, and the Diptera Nemocera, the mid-intestine and 
some other larval organs are greatly modified, but there is no general 
histolysis. On the other hand, in the Diptera Brachycera, there is a 
general histolysis. In Mtisca all organs break down and are reformed 
except the central nervous system, the heart, the reproductive organs, 
and three pairs of thoracic muscles. Regarding the extent of the 
transformations in the other orders where the metamorphosis is com- 
plete we have, as yet, but little data. 

For a more detailed and exhaustive discussion of the morphology 
of insects the special student should consult the authoritative book 
by R. E. Snodgrass, "Principles of Insect Morphology" (1935). 



PART II 

THE CLASSIFICATION AND THE LIFE- 
HISTORIES OF INSECTS 



Class HEXAPODA 

The Insects 

The members of this class are air-breathing arthropods, with distinct 
head, thorax, and abdomen. They have one pair of antennce, three pairs 
of legs, and usually one or two pairs of wings in the adidt state. In 
most adult insects the head bears a pair of compound eyes. The opening 
of the reproductive organs is near the caudal end of the body. 

The more general character of insects, together with their structure 
and morphology, has been discussed at some length in Part I of this 
book. It is now appropriate to consider the classification, habits and 
life histories of insects. Part II will therefore be devoted to a dis- 
cussion of the subclasses, orders, and families of this great group of 
animals. 

The class Hexapoda is divided into two subclasses, the small 
wingless insects, Apterygota, and the winged insects, Pterygoia. 
The subclass Apterygota is a small one, containing but three orders 
(four by some authors) and mostly unfamiliar forms except to those 
especially interested in these tiny creatures. The subclass Pterygota 
is a very large group including all of the remaining twenty-three 
orders discussed in this book. This subclass contains all of the more 
familiar forms, such as grasshoppers, beetles, butterflies, moths, 
flies, wasps, and bees. 



CHAPTER V 

THE SUBCLASSES AND THE ORDERS OF THE 
CLASS HEXAPODA 

Insects constitute one of the classes of the Arthropoda, that 
division of the animal kingdom in which the body is composed of a 
series of more or less similar segments and in which some of these 
segments bear jointed legs. This class is known as the Hexapoda. 

The distinctive characteristics of the Class Hexapoda and its 
relation to the other classes of the Arthropoda are discussed in the 
first chapter of this work; we have now to consider the division of 
this class into subclasses and orders. 

The orders that constitute the Hexapoda represent two well-marked 
groups; this class is divided, therefore, into two subclasses. This 
division was first proposed by Brauer ('85), who recognized the fact 
that while the wingless condition of certain insects, the fleas, lice, 
bird-lice, and the wingless members of orders in which the wings are 
usually present, is an acquired one, the wingless condition of the 
Thysanura and Collembola is a primitive one. In other words, from 
the primitive insects, which were wingless, there were evolved on the 
one hand the orders Thysanura and Collembola, which remained 
wingless, and on the other hand, a winged form from which have 
descended all other orders of insects. 

An extended study of the wings of insects has shown that the 
wings of all of the orders of winged insects are modifications of a 
single type ; it is believed, therefore, that all of the orders of winged 
insects have descended from a common winged ancestor. As to the 
lice, bird-lice, and fleas, the relation of each of these groups to certain 
winged insects, as shown by their structure, has led to the belief that 
their wingless condition is an acquired one, being the result of parasitic 
habits. The lice or Anoplura are commonly regarded as closely 
allied to the Homoptera and Heteroptera ; the bird-lice or Mallophaga 
to the Corrodentia; and the fleas or Siphonaptera to the Diptera. 
Hence these wingless insects are placed with the winged insects in a 
single subclass. 

The two subclasses thus recognized were named by Brauer the 
Apter^^gogenea and the Pterygogenea respectively. The cumber- 
someness of these names led to the substitution for them of the 
shorter names Apterygota and Pter3'gota. The Apterygota includes 
the orders Thysanura and Collembola; and the Pterygota, all other 
orders of insects. Some writers regard the Th\'sanura and Collem- 
bola as suborders of a single order, which they term the Aptera. 

The distribution of insects into orders is based on the classification 
of Linnaeus, as set forth in his "Systema Naturse" (i 735-1 768). 
Linnaeus, who has been called the Adam of zoological science, divided 

(206) 



HEX A POD A 207 

his class Insecta into seven orders; these he named Coleoptera, 
Hemiptera, Lepidoptera, Neuroptera, H}Tnenoptera, Diptera, and 
Aptera, respectively. 

Since the time of Linnasusmany modifications of his classification 
of insects have been proposed; and new ones are constantly appear- 
ing. The result is that now there is a great lack of uniformity in the 
classification used by dift'erent writers. 

The modifications of the Linnaean distribution of insects into 
orders are based on the belief that in certain cases Linnteus grouped 
into a single order forais that really represent two or more distinct 
orders. The result has been a great increase in the number of orders 
recognized. 

Linnajus included in his class Insecta, under the order Aptera, 
not only wingless insects but also arachnids, crustaceans, centipedes, 
and millipedes. The animals thus grouped by LinncTus are now dis- 
tributed into several classes; and to the class composed of the animals 
now commonly known as insects, those characterized by the posses- 
sion of only six legs, the term Hexapoda is commonly applied. Some 
writers, however, apply the term Insecta to the class of insects as 
now limited. 

Some of the more recently recognized orders of insects are repre- 
sented among living insects by comparatively few species; but in 
each case the structure of the insects included in the group is so differ- 
ent from that of all other insects that we are led to belie\'e that they 
represent a division of the class Hexapoda that is of ordinal value. 

There are given below the names of the orders of insects recognized 
in this work. The sequence in which these orders are discussed is of 
necessity a more or less arbitrary one. In general the plan adopted 
here is to make the series an ascending one; that is, the more gen- 
eralized or primitive insects are placed first and the more highly 
specialized ones later in the series; but as the different orders of 
insects have been specialized in very different ways, the relative de- 
grees of their specialization cannot be shown by arranging them in a 
single linear series, as must be done in a book. To indicate the 
different wa}-s in which the dift'erent members of a group have been 
specialized and the relative rank of those specialized in a similar way, 
use must be made of a diagram representing a genealogical tree. 
Many such diagrams have been made, but no one of them has re- 
ceived general acceptance; much remains to be learned before such 
a diagram can be made that will inspire confidence in its accuracy. 

In the course of the preparation of a special treatise on the wings 
of insects (Comstock ' 1 8 a) , I wrote a table indicating the more strik- 
ing of the methods of specialization of the wings characteristic of 
each of the orders of winged insects; and in the discussion of the 
different orders, I followed the sequence indicated by tnis table. In 
doing this I did not advocate the basing of a classification of insects 
upon the characters presented by the wings alone, but merely made 
use of these characters for the purposes of that work. 



208 AN INTRODUCTION TO ENTOMOLOGY 

A renewed study of the relationships of the different orders to each 
other, in which an effort has been made to correlate other characters 
with those presented by the wings, has not indicated the desirability 
of changes in the sequence of the orders indicated in that table, ex- 
cept in the allocation of those orders in which wings are wanting. 

The importance of the wings of insects for taxonomic purposes 
was early recognized by entomologists, as is well shown by the fact 
that the names of the Linnsean orders are all drawn from the nature 
of the wings, except one, Aptera, and that from the absence of wings. 

The different methods of specialization of the wings arose very 
early in that part of the geological history of insects that is known 
to us. And as most of the fossil remains of the older insects consist 
of wings, we are forced to depend very largely on the characters 
presented by these organs for data regarding the separation of the 
primitive insects into the groups from which the orders of recent 
insects have been developed. But in characterizing the orders as they 
now exist all the results of the study of the structure of insects and 
of their transformations are available. 

Aside from the structure of the wings, the characters most used 
in characterizing the orders of insects are those presented by the 
structure of the mouth-parts and the nature of the post-embryonic 
development. While these characters are of value in defining the 
orders, but little use has been made of them, as yet, in working out 
the lines of descent of the various orders from the primitive insects. 

The primitive insects had chewing mouth-parts and this type has 
been retained in the greater mmiber of the orders. But although 
many detailed accounts of the structure of the mouth-parts of chew- 
ing insects have been published, no one has worked out the various 
ways in which they have been specialized in such a manner as to in- 
dicate the phylogeny of the orders. 

Several different types of sucking mouth-parts exist among living 
insects; but these are apparently of comparatively late origin, and 
while they are of great value in defining the orders in which they 
occur, they do not afford characters for determining the primitive 
divisions of the Pterygota. 

The nature of the post-embryonic development of insects, like 
the structure of the mouth-parts, affords characters for defining the 
orders of recent insects, but is of little value in determining the 
phylogeny of the orders. 

The primitive insects doubtless developed without any marked 
metamorphosis as do the Thysanura and Collembola of today. With 
the development of wings, there arose that type of development 
known as gradual metamorphosis, and this type is retained by eight 
of the orders recognized in this work. Incomplete metamorphosis 
is the result of a sidewise development of the immature instars of the 
insects exhibiting it, in order to fit them for life in the water, and it 
doubtless arose independently in each of the three orders in which 
it occurs; it is therefore an ordinal characteristic in each case and not 
one indicating a natural group of orders. This is also true of com- 



HEX A POD A 209 

plete metamorphosis, which also doubtless arose independently in 
different divisions of the insect series, as, for example, intheNeurop- 
tera, which it is believed is a very ancient order, the origin of which 
was much earlier than the attainment of complete metamorphosis. 

TABLE OF THE METHODS OF SPECIALIZATION OF THE WINGS CHARACTERISTIC 
OF THE ORDERS OF WINGED INSECTS* 

This table is merely the result of an eflfort to indicate the more striking of 
the methods of specialization of the wings characteristic of each of the orders 
of insects. It is not a key for determining the orders of insects. It is not avail- 
able for this purpose; because, in many cases, the wings of an insect do not 
show the type of specialization characteristic of the order to which the insect 
belongs. Thus, for example, while the most characteristic modification of the 
courses of the wing-veins in the Diptera and Hymenoptera is due to the coales- 
cence of veins proceeding from the margin of the wing towards the base of the 
wing, there is no indication of this type of coalescence of veins in some of the 
nemocerous Diptera. 

A. Wings specialized by the development of supernumerary veins in the preanal 
area. 
B. Supernumerary veins of the accessory type. 
C. Wings developed externally. 

D. Wings retained throughout life. Wings without a striking contrast 
in the thickness of the veins of the anterior part of the wing and those 

of the middle portion Orthoptera 

DD. Wings deciduous, there being near the base of each wing a trans- 
verse suture along which the wing is broken off after the swarming 
flight. Wings with the veins of the anterior part of the wing greatly 
thickened and those of the middle portion reduced to narrow lines 

ISOPTERA 

CC. Wings developed internally Neuroptera 

BB. Supernumerary veins of the intercalary type. 

C. Flight -function cephalized; the hind wings being greatly reduced 

in size Ephemerida 

CC. Flight-function not cephalized; the hind wings as large as or larger 

than the fore wings Odonata 

AA. Wings speciaHzed by a reduction in the number of veins in the preanal 
area. 
B. Wings developed externally. 

C. The two pairs of wings similar in texture. 

D. With the tendency to develop accessory veins retained. . Plecoptera 
DD. With the tendency to develop accessory veins in the preanal area 
lost, 
E. With the courses of some of the longitudinal veins modified so 

that they function as cross-veins Corrodentia 

EE. The transverse bracing of the wing attained in the usual way. 
F. The veins of the wing bordered with dark bands.. .Embiidina 
FF. The veins of the wing not bordered with dark bands. 

G. Wings long and narrow, supplemented by a wide fringe of 

hairs Thysanoptera 

GG. Wings not greatly narrowed and not supplemented by a 

wide fringe of hairs Homoptera 

CC. The front wings more or less thickened. 

D. The front wings not greatly reduced in length as compared with 
the hind wings. 

E. The front wings thickened throughout Homoptera 

EE. The front wings thickened at the base, the terminal portion 

membranous Heteroptera 

DD. The front wings greatly reduced in length Dermaptera 

*From "The Wings of Insects," pp. 120-122. 



210 AN INTRODUCTION TO ENTOMOLOGY 

BB. Wings developed internally. 
C. Fore wings greatly thickened. 

D. Fore wings modified so as to serve as covers of the posterior wings 

COLEOPTERA 

DD. Fore wings reduced to slender, leathery, club-shaped appendages 

Strepsiptera 

CC. The two pairs of wings similar in texture. 

D. With the tendency to develop accessory veins retained. .Mecoptera 
DD. With the tendency to develop accessory veins lost. 

E. The most characteristic method of reduction of the wing-veins 
of the preanal area being by coalescence outward. 
F. Anal veins of the fore wings tending to coalesce at the tip. Wings 

usually clothed with hairs Trichoptera 

FF. Anal veins of the fore wings not tending to coalesce at the 

tip. Wings clothed with scales Lepidoptera 

EE. The most characteristic method of reduction of the wing-veins 
of the preanal area being by coalescence from the margin of the 
wing inward. 

F. With only one pair of wings Diptera 

FF. With two pairs of wings Hymenoptera 

The sequence in which the orders of insects are discussed in the 
following chapters has been determined by the above table. This 
sequence, lil^e all linear arrangements of groups of organisms, is more 
or less arbitrary. Thus while there is an effort to place first the more 
generalized orders and later those that are more specialized, the 
putting together of orders exhibiting the same type of specialization 
results in some cases in the placing of comparatively generalized 
forms after those that are obviously more highly specialized. The 
position of the Plecoptera is an illustration of this. The insects of 
this order are evidently more generalized than, for example, the 
Neuroptera or the Odonata, which are placed earlier in the linear 
series. 

The comparatively high position assigned to the Plecoptera is, 
however, only apparent. A reference to the table will show that the 
orders of insects are grouped in two series, "A" and "AA". Under 
"A" are placed those orders in which the wings are specialized by 
addition in the preanal area, and under "AA" those orders in which the 
wings are specialized by reduction in the preanal area. Each of these 
series includes some quite generalized insects and others that are 
highly specialized. The completion of the discussion of the first series 
before taking up the second series results in the generalized members 
of the second series following the highly specialized members of the 
first series. 

The more generalized members of these two series, the Orthoptera 
of the first series and the Plecoptera of the second series, are probably 
more closely allied to each other than is either of these orders to the 
more specialized orders of the series in which it is placed; the two 
series arose from a common starting point, the Palaeodictyoptera, but 
have widely diverged in the course of their development. 

An even more striking illustration of the difficulty of indicating 
the relative ranks of orders by the use of a single linear series is the 
position of the Isoptera in the above table. This order is a very 



HEX APOD A 211 

ancient one; it separated from the Palasodictyoptera before definite 
cross-veins in the wings had been developed and has not attained 
them. It is placed in the table next to the Orthoptera because the 
wings are specialized by the development of supernumerary veins of 
the accessory t3pe and are developed externally; but the peculiar 
specialization of the wings is very different from that of the Orthop- 
tera as is indicated in the table. And in other respects the termites 
have reached a stage of development far in advance of that shown by 
any of the Orthoptera. They have attained a social mode of life, 
with the correlated separation of the species into several castes and 
the development of remarkable instincts. In this respect they rival 
the social H^Tnenoptera. 

In fact the living members of each of the orders of insects must be 
regarded as a group of organisms representing the results of speciali- 
zation in a direction different from that of any other order; and to 
attempt to decide which order is the "highest" seems as futile as the 
discussion by children of the question: "Which is better, sugar or 
salt?" The "list below indicates the sequence in which the orders are 
discussed in the following chapters. 



THE SUBCLASSES AND ORDERS OF THE HEXAPODA 

SUBCLASS A'^TFRYGOTA. — Wingless insects in which the wingless condition is 
believed to oe a primitive one, there being no indication that they descended 
from winged ancestors. 

ORDER PROTURA. — The Telson-tails. p. 218. 

ORDER THYSANURA. — The Bristle-tails. p. 219. 

ORDER COLLEMBOLA. — The Spring-tails. p. 225. 

SUBCLASS PTERYGOTA. — Winged insects and wingless insects in which the 
wingless condition is believed to be an acquired one. 

ORDER ORTHOPTERA. — The Cockroaches, Crickets, Grasshoppers, and others, 
p. 230. 

ORDER ZORAPTERA. — The genus Zorotypus. p. 270. 

ORDER isoPTERA. — The Termites or White Ants. p. 273. 

ORDER NEUROPTERA. — The Dobson, Aphis-lions, Ant-lions, and others, p. 281. 

ORDER EPHEMERiDA. — The May-flies. p. 303. 

ORDER ODONATA. — The Dragon-flies and ths Damsel-flies, p. 314. 

ORDER PLECOPTERA. — The Stone-flies. p. 325. 

ORDER CORRODENTIA. — The Psocids. p. 33 1. 

ORDER MALLOPHAGA. — The Bird-lice. p. 335. 
ORDER EMBUDINA. — The Embiids. p. 338. 
ORDER THYSANOPTERA. — The Thrips. p. 341. 
ORDER ANOPLURA. — The Lice. p. 347. 

ORDER HOMOPTER.\. — The Cicadas, Leaf-hoppers, Aphids, Scale-bugs, and 
others, p. 394. 

ORDER HEMiPTERA. — The True Bugs. p. 350. 

ORDER DERMAPTERA. — The Earwigs. p. 460. 

ORDER COLEOPTERA. — The Beetles, p. 464. 

ORDER STREPSIPTERA. — The Twisted Winged Insects, p. 546. 

ORDER MECOPTERA. — The Scorpion-flies. p. 550. 

ORDER TRICHOPTERA. — The Caddice-flies. p. 555. 

ORDER LEPIDOPTERA. — The Moths, the Skippers, and the Butterflies, p. 571. 

ORDER DIPTERA. — The Flies. p. 773. .. . -.---. 

ORDER SIPHONAPTERA. — The Fleas. p. 877. '^tSlQii^A/ 

ORDER HYMENOPTERA. — The Bees, Wasps, Ants, and others, p. 884. lXV_ -_^ ^ '• 



t 




212 AN INTRODUCTION TO ENTOMOLOGY 

TA BLE FOR DETERMINING THE ORDERS OF THE HEX A POD A 

This table is merely intended to aid the students in determining to which of 
the orders a specimen that he is examining belongs. No effort has been made to 
indicate in the table the relation of the orders to one another. 

A. Winged. (The wing-covers, Elytra, of beetles and of earwigs are wings.) 
B. With two wings. 

C. Wings horny, leathery, or parchment-like. 

D. Mouth-parts formed for sucking. Wings leathery, shortened, or 

membranous at the tip. p. 350 Hemiptera 

DD. Mouth-parts formed for biting. Jaws distinct. 

E. Wings horny, without veins. Hind legs not fitted for jumping. 

p. 464 COLEOPTERA 

EE. Wings parchment-lilce with a network of veins. Hind legs fitted 

for jumping, p. 230 Orthoptera 

CC. Wings membranous. 
. D. Abdomen with caudal filaments. Mouth-parts vestigial. 

E. Halteres wanting, p. 308 Ephemerida 

EE. Halteres present (males of Coccidas). p. 394 Homoptera 

DD. Abdomen without caudal filaments. Halteres in place of second 

wings. Mouth-parts formed for sucking, p. 773 Diptera 

BB. With four wings. 

C. The two pairs of wings unlike in structure. 

D. Fore wings reduced to slender club-shaped appendages; hind wings 
fan-shaped with radiating veins. Minute insects, p. 546. .Strepsiptera 
DD. Front wings leathery at base, and membranous at tip, often over- 
lapping. Mouth-parts formed for sucking, p. 350. . .Hemiptera 
DDD. Front wings of same texture throughout. 

E. Front wings horny or leathery, being veinless wing-covers. (Ely- 
tra). 
F. Abdomen with- caudal appendages in form of movable forceps. 

p. 460 Dermaptera 

FF. Abdomen without forceps-like appendages, p. 464. Coleoptera 

EE. Front wings leathery or parchment-like with a network of veins. 

F. Under wings not folded; mouth-parts formed for sucking. 

G. Beak arising from the front part of the head. p. 350. Hemiptera 

GG. Beak arising from the hind part of the lower side of the head. 

p. 394 Homoptera 

FF. Under wings folded lengthwise. Mouth-parts formed for 

chewing, p. 230 Orthoptera 

CC. The two pairs of wings similar, membranous. 

D. Last joint of tarsi bladder-like or hoof-like in form and without 

claws, p. 341 Thysanoptera 

DD. Last joint of tarsi not bladder-lilce. 

E. Wings entirely or for the greater part clothed with scales. Mouth- 
parts formed for sucking, p. 571 Lepidoptera 

EE. Wings naked, transparent, or thinly clothed with hairs. 

F. Mouth-parts arising from the hinder part of the lower surface of 
the head, and consisting of bristle-lil<;e organs inclosed in a jointed 

sheath, p. 394 Homoptera 

FF. Mouth-parts in normal position. Mandibles not bristle-like. 
G. Wings net-veined, with many veins and cross-veins. 
H. Tarsi consisting of less than five segments. 

I. Antennas inconspicuous, awl-shaped, short and slender. 
J. First and second pairs of wings of nearly the same length; 

tarsi three-jointed, p. 314 Odonata 

JJ. Second pair of wings either small or wanting; tarsi 
four-jointed, p. 308 Ephemerida 

II. Antenna usually conspicuous, setiform, filiform clavate, 
capitate, or pectinate. 

J. Tarsi two- or three- jointed. 

K. Second pair of wings the smaller. Pc 33 1 . Corrodentia 



HEX A POD A 213 

KK. Second pair of wings broader, or at least the 
same size as the first pair. p. 325. . . .Plecoptera 
JJ. Tarsi four-jointed; wings equal, p. 273. .Isoptera 
HH. Tarsi consisting of five segments. 

I. Abdomen with setiform, many-]ointed anal filaments. 
(Certain May-flies), p. 308 Ephemerida 

II. Abdomen without many-jointed anal filaments. 

J. Head prolonged into a trunk-like beak. p. 550.MECOPTERA 
J J. Head not prolonged into a beak. p. 281.. .Neuroptera 
GG. Wings with branching veins and comparatively few cross- 
veins, or veinless. 
H. Each of the veins of the wing extending along the middle of 

a brown line. p. 338 Embiidina 

HH. Wings not marked with brown lines. 

I. Tarsi two-or three- jointed. 

J. Hind wings smaller than the fore wings. 

K. Cerci present; body less than three millimeters in 

length, p. 270 ZORAPTERA 

KK. Cerci absent; larger insects, p. 331..C0RRODENTIA 

JJ. Posterior wings as large as or larger than the anterior 

ones. (Certain Stone-flies), p. 325 Plecoptera 

II. Tarsi four- or five-jointed. 

J. Abdomen with setiform, many-]ointed anal filaments. 

(Certain May-flies), p. 308 Ephemerida 

JJ. Abdomen without many-jointed anal filaments. 
K. Prothorax horny. First wings larger than the second, 
naked or imperceptibly hairy. Second wings without, 
or with few, unusually simple, veins. Jaws (mandibles) 
well developed. Palpi small, p. 884. . . . Hvmenoptera 
KK. Prothorax membranous or, at the most, parchment- 
like. Second wings as large as or larger than the 
first, folded lengthwise, with many branching veins. 
First wings naked or thinly clothed with hair. Jaws 
(mandibles) inconspicuous. Palpi long. JVIoth-like 

insects, p. 555 Trichoptera 

AA. Wingless or with vestigial or rudimentary wings. 

B. Insects with a distinct head and jointed legs, and capable of locomotion. 
C. Aquatic insects. 

D. Mouth-parts fitted for piercing and sucking. 

E. Free-swimming nymphs, p. 350 Hemiptera 

EE. Larvae parasitic in sponges (Sisyridae). p. 281 Neuroptera 

DD. Mouth-parts fitted for chewing. 

E. Either somewhat caterpillar-like larvae that live in portable cases or 
campodeiform larvae that spin nets for catching their food. (Caddice- 

worms). p. 555 Trichoptera 

EE. Neither case-bearing nor net-spinning larvae. 

F. Naiads, that is, immature insects that resemble adults in having 
the thorax sharply differentiated from the abdomen, and, except in 
very young individuals, with rudimentary wings. 
G. Lower lip greatly elongated, jointed, capable of being thrust for- 
ward, and armed at its extremity with sharp hooks, p. 314.ODONATA 
GG. Lower lip not capable of being thrust forward. 

H. Usually with filamentous tracheal gills on the ventral side 

of the thorax, p. 325 Plecoptera 

HH. Tracheal gills borne by the first seven abdominal seg- 
ments, p. 308 Ephemerida 

FF. Larvae, that is, immature forms that do not resemble adults in 
the form of the body, and in which the developing wings are not 
visible externally. 
G. Several segments of the abdomen fiu-nished with prolegs. 

p. 571 Lepidoptera 

GG. With only anal prolegs or with none. 



214 AN INTRODUCTION TO ENTOMOLOGY 

H. With paired lateral filaments on most or on all of the ab- 
dominal segments. (SiaHdas). p. 281 Neuroptera 

See also Haliplidas and Gyrinidas. p. 464 Coleoptera 

HH. Without paired lateral filaments on the abdomen, p. 464. 

Coleoptera 

CC. Terrestrial insects. 
D. External parasites. 

E. Infesting the honey-bee. (Braula). p. 773 Diptera 

EE. Infesting birds or mammals. 

F. Body strongly compressed. (Fleas), p. 877 Siphonaptera 

FF. Body not strongly compressed. 

G. Mouth-parts formed for chewing. (Bird-lice), p. 335. 

Mallophaga 

GG. Mouth-parts formed for piercing and sucking. 

H. Antennre inserted in pits, not visible from above. (Pupi- 

para). p. 773 Diptera 

HH. Antennae exserted, visible from above. 
G. Tarsi with a single claw which is opposed by a toothed pro- 
jection of the tibia. (Lice), p. 347 Anoplura 

GG. Tarsi two-clawed, p. 350 Hemiptera 

DD. Terrestrial insects not parasites. 

E. Mouth-parts apparently retracted within the cavity of the head so 
that only their apices are visible, being overgrown by folds of the genae. 
F. Abdomen consisting of ten or eleven segments. (Campodeidce and 

Japygidae). p. 220 Thysanura 

FF, Abdomen consisting of not more than six segments, p. 225. 

Collembola 

EE. Mouth-parts mandibulate, either fitted for chewing or with 
sickle-shaped mandibles formed for seizing prey. (See also EEE.) 
F. Larvffi with abdominal prolegs. 

G. Prolegs armed at the extremity with numerous minute hooks. 

(Caterpillars), p. 571 Lepidoptera 

GG. Prolegs not armed with minute hooks. 

H. With a pair of ocelH, one on each side. (Larvas of saw-flies). 

p. 884 Hymenoptera 

HH. With many ocelli on each side of the head. p. 550 

Mecoptera 

FF. Without abdominal prolegs. 

G. Body clothed with scales. (Machihdas and Lepismatidae). 

p. 220 Thysanura 

GG. Body not clothed with scales. 
H. Antennae long and distinct. 

I. Abdomen terminated by strong movable forceps, p. 460. 
Dermaptera 

II. Abdomen not terminated by forceps. 

J. Abdomen strongly constricted at base. (Ants. etc.). 

p. 884 Hymenoptera 

JJ. Abdomen not strongly constricted at base. 

K. Head with a long trunk-like beak. {Boreus). p. ^50. 

Mecoptera 

KK. Head not prolonged into a trunk. 

L. Insects of small size, more or less louse-like in form, 
with a very small prothorax, and without cerci. 

(Book-lice and Psocids). p. 331 CorrodExNTIA 

LL. Insects of various forms, but not louse-like, 
prothorax not extremely small; cerci present. 
M. Hind legs fitted for jumping, hind femora en- 
larged. (Wingless locusts, grasshoppers, and 

crickets), p. 230 Orthoptera 

MM. Hind femora not greatly enlarged, not fitted 
for jumping. 



HEX A POD A 215 

N. Prothorax much longer than the mesc thorax; 
front legs fitted for grasping prey. (Mantidas). 

p. 230 Orthoptera 

NN. Prothorax not greatly lengthened. 

O. Cerci present; antennas usually with more 
than fifteen joints, often many-jointed. 
P. Cerci with more than three joints. 

Q. Body flattened and oval. (Blattidas). 

p. 230 Orthoptera 

QQ. Body elongate. 

R. Head very large. (Termopsis) . p. 273. 

ISOPTERA 

RR. Head of moderate size. p. 268. 

Grylloblattid^ 

PP. Cerci short, with one to three joints. 

Q. Body hnear with very long linear legs. 

(Walking-sticks), p. 230 ... Orthoptera 

QQ. Body elongate or not, if elongate the 

legs are not linear. 

R. Body elongate, front tarsi with first 

joint swollen, p. 338. . . Embiidina 

RR. Front tarsi not enlarged. 

S. Minute insects, less than 3 mm, 
in length; antennae nine-jointed. 

p. 270 Zoraptera 

SS. Larger insects,; antennae usually 
more than nine- jointed. (White-ants) . 

p. 273 Isoptera 

00. Cerci absent; antennse usually with eleven 

joints, p. 464 Coleoptera 

HH. Antennae short, not pronounced; larval forms. 

I. Body cylindrical, caterpillar-like. p. 550.MECOPTERA 

II. Body not caterpillar-like. 

J. Mandibles sickle-shaped; each mandible with a furrow 
over which the maxilla of that side fits, the two forming 
an organ for piercing and sucking. (Ant-lions, aphis- 
lions, hemerobiids). p. 281 Neuroptera 

JJ. Mouth-parts not of the ant-lion type. 

K. Larva of Raphidia. p. 281 Neuroptera 

KK. Larvae of beetles, p. 464 Coleoptera 

EEE. Mouth-parts haustellate, fitted for sucking; mandibles not 
sickle-shaped. 
F. Body covered with a waxy powder or with tufts or plates of wax. 

(Mealy-bugs, Orthezia). p. 350 Hemiptera 

FF. Body more or less covered with minute scales, or with thick- 
long hairs; proboscis if present coiled beneath the head: (Moths). 

p. 57 1 Lepidoptera 

FFF. Body naked, or with isolated or bristle-like hairs. 

G. Prothorax not well developed, inconspicuous or invisible 

from above, p. 773 Diptera 

GG. Prothorax well developed. 

H. Last joint of tarsi bladder-like or hoof-like in form and 
usually without claws; mouth-parts forming a triangular 

unjointed beak. p. 550 Thysanoptera 

HH. Last joint of tarsi not bladder-like, and ftunished with one 
or two claws; mouth-parts forming a slender; usually 
jointed beak. 
I. Beak arising from the front part of the head. p. 350. 

Hemiptera 

II. Beak arising from the back part of the head. p. 394 . . . 

.0 HOMOPTERA 



216 AN INTRODUCTION TO ENTOMOLOGY 

BB. Either without a distinct head, or without jointed legs, or incapable of 
locomotion. 
C. Forms that are legless but capable of locomotion; in some the head is 
distinct, in others not. Here belong many larvae representing several of 
the orders, and the active pupse of mosquitoes and certain midges. It is 
impracticable to separate them in this key. 
CC. Sedentary forms, incapable of locomotion. 

D. Small abnormal insects in which the body is either scale-like or gall- 
like in form, or grub-like clothed with wax. The waxy covering may be 
in the form of powder, or large tufts or plates, or a continuous layer, or of 
a thin scale, beneath which the insect lives. (Coccidse). p. 350.HEMIPTERA 
DD. Pupae, the inactive stage of insects with a complete metamor- 
phosis; capable only of a wriggling motion, and incapable of 
feeding. 
E. Obtected pupae, pupae in which the legs and wings are glued to the 
surface of the body; either in a cocoon or naked, p. 571 . Lepidoptera 
EE. Coarctate pupae, pupae enclosed in the hardened larval skin. 

p. 773 DiPTERA 

EEE. Exarate pupae, pupas that have the legs and wings free; either in 
a cocoon or naked. This type of pupa is characteristic of all of the 
orders in which the metamorphosis is complete except the Lepidop- 
tera and Diptera. 



The order Protura does not occur in the foregoing table because 
it has only now, in this edition (1936), been placed among the 
Hexapoda. Since the members of the order are uncommon insects 
rarely met with it did not seem advisable to incur the added expense 
of rearranging and reprinting a large part of the table. 



CHAPTER VI 

Subclass I. APTERYGOTA 
Wingless Insects 

The members of this subclass are small wingless insects in which 
the wingless condition is believed to be a primitive one, there being no 
indication that they have descended from winged ancestors. The month- 
parts vary. In some they are sucking, in others chewing. The meta- 
morphosis is always slight and in some cases absent. 

This subclass contains but the three orders, Protura, Thysanura, 
and Collembola. These insects are all primitive and usually general- 
ized. They are all small and wingless and because of their usually 
concealed habits are not as generally known as the winged forms. 
They are widely distributed and about 1200 species are now known. 
Probably many more remain to be discovered. A characteristic 
feature of these primitive insects is the abdominal appendages, 
especially the abdominal styli present in the Machilidae and in others 
of the Thysanura. 



(217) 



CHAPTER VII 
ORDER PROTURA 

The Tclson-Tails 

The members of this order are small arthropods in which the body is 
elongate, as in the Thysanura, fusiform, pointed behind, and depressed; 
it may be greatly extended and retracted. The antennce, cerci and 
compound eyes are absent. The oral apparatus is suctorial, and consists 
of three pairs of gnathites. There are three pairs of thoracic legs, and 
three pairs of vestigial abdominal legs. The abdomen is composed of 
eleven segments and a telson. The opening of ihe reproductive organs is 
unpaired, and near ihe hind end of the body. The head bears a pair of 
organs, termed pseitdocidi, the nature of which has not been definitely 
determined. The metamorphosis is slight, consisting of an increase in 
the number of abdominal segments. 

The known members of this order are very small arthropods, 
the body measuring fron one fiftieth to three-fiftieths of an inch in 
length. The form, of the body is shown by Figure 36, p. 25. 

These exceedingly interesting creatures are found in damp situa- 
tions, as in the humus of gardens. They are widely distributed: 
they are now known to occur in India, England, Italy, and other 
European countries. A number of species have been described from 
the southwestern United States. 

The mouthparts are withdrawn into the head and the mandibles 
are stylet-like and fitted for piercing. In the newly hatched insect 
the abdomen is 9-segmented, but during later growth three more 
segments are added between the last two segments. This mode of 
change in form is known as anamorphosis. 

The systematic position of the Protura is still unsettled. The 
differentiated thorax with three pairs of legs and the form of the 
mouthparts are characteristic of insects. The lack of antennae 
and the intercalary addition of body segments during growth (ana- 
morphosis) are very unlike insects. The name Protura refers to the 
last telson-like segment of the abdomen. 

The order contains two families as follows : 

Family i. Acerentomid^, in which the tracheae and spiracles 
are absent and the second and third abdominal appendages are i- 
jointed. This family includes the two genera Acerentomon and 
Acerentidus. 

Family 2. Eosentomidae, in which tracheae are present with two 
pairs of thoracic spiracles and the second and third abdominal 
appendages are 2-jointed. This family includes the genus Eosen- 
tomon and probably Protapteron. 

(218) 



THYSANURA 



219 



ORDER THYSANURA* 



The Bristle-Tails 

The members of this order are wingless insects in which the wingless 
condition is believed to he a primitive one, there being no indication that 
they have descended from winged ancestors; the month-parts ore formed 
for cheiving; and the adult insects resemble the young in form. In these 
three respects, these insects resemble the next order, the Collembola; but 

they differ from the Collembola in 
that the abdominal segments are 
not reduced in number and the 
cerci are usually filiform and 
many-jointed; some members of 
the order have also a caudal fila- 
ment. 

The members of this order 
are known as bristle-tails, a 
name suggested by the pres- 
ence, in most of them, of either 
two or three many- jointed 
filiform appendages at the cau- 
dal end of the body (Fig. 221, 
c, and m f) . The paired caudal 
appendages are the cerci; the 
median one, when three are 
present, is the median caudal 
filament, a prolongation of the 
eleventh abdominal segment. 
In fdpyx (Fig. 222), the cerci 
are not jointed but are strong, 
curved appendages, resembling 
the forceps of earwigs. 

The bristle-tails are most 
often found under stones and 
other objects lying on the 
ground; but some species live 
in houses. While most species 
prefer cool situations, there is 
one, the fire-brat, that fre- 
quents warm ones, about fire- 
places and in bakehouses. The 
antennae are long and many- 
jointed. In the Machilidas 




Fig. 221. — Machilis, ventral aspect: c, cer- 
cus ; Ip, labial palpus ; mf, median caudal 
filament: mp, maxillary palpus; 0, ovi- 
positor; s, s, styli. 



"Thysanura: thysanos (Svpavos), a tassel; oiira {ovpd), the tail. 



220 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. 222. — Japyx sol- 
ifugus. (After Lub- 
bock.) 



(Machilts), the eyes are very perfect; for this reason, they are used 
in Chapter III to illustrate the structure of the compound eyes of 
insects. In all other Apterygota they are more or less degenerate or are 
lost entirely. In the Lepismatidas (Lepisma) , the degeneration of the 
eyes has progressed far, they being reduced to a group of a dozen 
ommatidia, on each side of the head. In the 
Campodeidas and the Jap}^gidae, the eyes have 
disappeared. The mouth-parts are formed for 
chewing ; those of Machilis will serve to illustrate 
their form. The mandibles are elongate with a 
toothed apex and a sub-apical projection teimi- 
nated by a grinding surface (Fig. 223, A); the 
paragnatha are comparatively well developed 
(Fig. 224); on the outer edge of each there is a 
small lobe, which Carpenter ('03), who regarded 
the organs as true appendages, believed to be a 
vestigial palpus, and at the tip there are two dis- 
tinct lobes, which this author homologized with 
the galea and the lacinia of a typical maxilla; the 
maxillge (Fig. 223, B) bear prominent palpi. 

In the Campodeidas and the Japygidas, the 
jaws are apparently sunk in the head. This con- 
dition is due to their being overgrown by folds of the genae. In the 
Machilidffi and the Lepismatidas the jaws are not overgrown; these 
two families are known, 
on this account, as the 
Ectotrophi or Ectotro- 
phous Thysanura; while 
the Campodeidas and the 
Japygidas are grouped 
together as the Ento- 
trophi or Entotrophous 
Thysanura. The over- 
growing of the mouth- 
parts by folds of the 
gense is characteristic of 
the Collembola also and 
is discussed more fully in 
the next chapter. 

The three thoracic 
segments are distincth' 
separate. There is noth- 
ing in the structure of 
the thorax to indicate 
that these insects have 
descended from winged 

ancestors. The three pairs of legs are well developed. In the genus 
Machilis the cox^ of the second and third pairs of legs each bears a 
stylus (Fig. 221, s). 




Fig. 223. — A, mandibles of Machilis; B, maxilla 
of Machilis. (After Oudemans.) 



THYSANURA 



221 



The abdomen consists of eleven segments. The eleventh segment 
bears the cerci, which are filiform and many-jointed except in th(j 
Japygidge, where they are forceps-like. In the 
Machilidee and the Lepismatids the eleventh 
abdominal segment bears a long, many-jointed 
median caudal filament; styli and eversible 
ventral sacs are also usually present ; these vary 
in number in difi'erent genera. 

The styli are slender appendages (Fig. 221, 
s). Each stylus consists of two segments, a 
very short basal one and a much longer termi- 
nal one. The maximimi number of styli is 
found in Machilis (Fig. 221), where they are 
borne by the second and third thoracic legs 
and the second to the ninth abdominal seg- 
ments. In Lepisma there are only three pairs; 
these are borne by the seventh, eighth, and 
ninth abdominal segments. 

The abdominal styli are borne by large 
plates, one on each side of the ventral aspect 
of each abdominal segment. These plates are 
termed coxites, as they are believed to be flat- 
tened coxae of abdominal legs which have otherwise disappeared. 

A result of the large size and position of the coxites is a reduction 
in the size of the sternum in the abdominal segments. This is well 
shown in Machilis (Fig. 221) ; in the first seven abdominal segments, 
there is in each a median triangular sclerite; this is the stemimi; in 
the eighth and ninth segments no sternum is visible. 




Fig. 224. — One of the 
paragnatha of Ma- 
chilis. (After Car- 
penter.) 




Fig. 225. — Cross-section of an abdominal segment of Machilis showing the 
styli and the ventral sacs. The ventral sacs of the left side are retracted ; those 
of the right side, expanded. (After Oudemans.) 

In the families Machilidas and Lepismatidas the females have an 
ovipositor, which consists of two pairs of filiform gonapophyses aris- 
ing from between the coxites of the eighth and ninth aiadominal 
segments respectively. 



222 



AN INTRODUCTION TO ENTOMOLOGY 



The ventral sacs are sac-like expansions of the wall of the coxites 
which can be everted, probably by blood -pressure, and are withdrawn 
into the cavity of the coxite by muscles (Fig. 225). In Figure 221, 
the openings into the retracted ventral sacs are represented ; there is 
one pair in the first abdominal seg- 
ment; two pairs in each of the four 
following segments; and a single pair 
each in the seventh and eighth ab- 
dominal segments. In Lepisma the 
ventral sacs are wanting. The func- 
tion of the ventral sacs has not been 
definitely determined; but it seems 
probable that they are blood-gills. 
The presence in the Thysanura of 
styli and of ventral sacs, which are 
evidently homologous with those of 
the Symphyla, is an indication of 
the primitive condition of these 
insects. The generalized form of 
the reproductive organs of the Thy- 
sanura is another indication of this. 
In Japyx the ovarian tubes have a 
metameric arrangement (Fig. 226); 
and in Machilis (Fig. 227) we find an 
intermediate form between a metameric arrange- 
ment of the ovarian tubes and a compact ovary. 
These facts, and especially the presence of styli and 
ventral sacs, are opposed to the view held by some 
writers that the Thysanura are degenerate instead 
of primitive insects. It is true that degenerate fea- 
tures are present in the order, as the loss of eyes in 
Japyx and Campodea; but this loss is correlated with 
the life of these insects in dark places, like the loss of eyes in certain 
cave-beetles, and is not important in the determination of the 
zoological position of the order. 

The young of the Thysanura resemble the adults in form, there 
being no marked metamorphosis. In Campodea and Japyx the molt 
is partial (Grassi '89). 

This is a small order; less than twenty American species have 
been described. The classification is as follows : 



Fig. 226. — 
Ovary of Ja- 
pyx. (After 
Grassi.) 



Fig.227.— Ovary 
of Machilis: c, 
coxite of the 
eighth abdomi- 
nal segment; s, 
stylus; o, ovi- 
positor. (After 
Oudemans.) 



Suborder I. ECTOGNATHA 



Body usually clothed with scales; monthparts outside of the head, 
not overgrown with folds of the genae; caudal end of abdomen with three 
long, filiform appendages; compound eyes present. 

Family i, Machilidae. The abdominal tergites reflexed to the 
under surface so as to form an imbrication covering the sides of the 



THYSANURA 223 

coxites (Fig. 221). Compound eyes large and contiguous. Pro- 
thorax smaller than the mesothorax. Middle and hind legs with 
vStyli. Saltatorial insects. 

This family is represented by the genus Machilis, of which several 
species occur in North America. These insects are found in heaps of 
stones and in other concealed places; they are very active and leap 
with agility when disturbed. They are about 12 mm. in length. 

Family 2, Lepismatidae. Abdominal tergites not covering the 
sides of the coxites. Eyes small and distant. Prothorax as large 
as or larger than the mesothorax. Middle and hind legs without 
styli. Not saltatorial insects. 

The best-known representative of this family is the silverfish or 
fish-moth Leptsma sacchanna (Fig. 228). It is silvery white with 
a yellowish tinge about the antennas and legs and measures about 




Fig. 228. — Lepisma 
saccharina. (After 
Lubbock.) 



8 mm. in length. It is often a troublesome pest in laundries, li- 
braries, and museums, as it injures starched clothes, the bindings of 
books, labels, and other things on which paste or gkie is used. The 
popular names were suggested by the clothing of scales with which 
the body is covered. 

Another common representative of this family is the fire-brat, 
Thermobia domcstica. This species resembles the fish-moth in 
general appearance except that it has dusky markings on its upper 
surface. It is remarkable for frequenting warm and even hot places 
about ovens, ranges, and fireplaces. 



224 



AN INTRODUCTION TO ENTOMOLOGY 



Suborder II. ENTOGNATHA* 

Body not clothed with scales; mouthparts within the head, being 
overgrown by folds of the gence; median caudal filament wanting; com- 
pound eyes absent. 

Family 3, Campodeid^. Cerci filiform, long 
and many-jointed; first abdominal segment 
without styli. 

The best-known member of this family is 
Campodea staphylmus (Fig. 229). It lives in 
damp places under stones, fallen trees, or in 
rotten wood and leaves. It is a very delicate, 
small, white insect, about 6 mm. in length. It 
has on the first abdominal segment a pair of 
appendages which occupy a position corre- 
sponding to that of the thoracic legs and each 
consists of two or three segments. 

Family 4, Projapygidae. Cerci short, 
rather stout, few-jointed; first abdominal seg- 
ment with styli. 

This family is represented by the genera 
Projapyx and Anajapyx. 

The species A. vesiculosus described by 
Silvestri may be considered representative. 

Family 5, Japygidae. Cerci forceps-like; 
styli present on first abdominal segment. 

This family is represented by the genus 

Jdpyx, of which two species have been found in 

this country. These insects can be recognized 

i7,-„ -,^„ ^ >, J by the forceps-like form of the cerci (Fig. 222). 

-big. 229. — Campodea rJ, n j i- .. • / 

staphylmus. (After They are small, delicate, uncommon msects 

Lubbock.) found under stones. 




*This suborder is raised to the rank of an order, Diplura, by Silvestri. Other 
systeraatists believe it should rank as a definite order. 



COLLEMBOLA 



225 



ORDER COLLEMBOLA* 

The Spring-Tails 

The members of this order resemble the Thysanura in being wingless 
insects in which the wingless condition is believed to be a primitive one, 
there being no indication that they have descended from winged ancestors, 
and in that the adtdt insects resemble the young in form. They differ 




Fig. 230. — Side view of Tomocerus plumbens: co, coUophore; c, catch; s spring. 
(Aftar Willem.) 

from the Thysanura as follows: the abdominal segments are reduced in 
number, there being only six of them; the first abdcnninal segment bears 
a ventral tube, the coUophore, furnished with a pair of eversible sacs which 
assist the insects in walking on smooth surfaces; 
the fourth abdominal segment usually bears a 
pair of appendages, which constitute a spring- 
ing organ; and the third abdominal segment 
usually bears a short pair of appendages, the 
catch, which hold the spring when it is folded 
under the abdomen. 

The common name spring-tails has been 
appHed to these insects on account of the 
caudal springing organ that is possessed by 
most members of the order. The spring- 
tails are minute insects, often of microscopic 
size and rarely as large as 5 mm. in length. 
Most of the species live on decaying matter. 
These insects are common under stones 
and decayed leaves and wood, in the chinks 
and crevices of bark, among moss, and on 
herbage in damp places. Sometimes they 
occur abundantly in winter on the surface 




Fig. 231. — An ommatid- 
ium of Podiira aqual- 
ica. (After Willem.) 



*Collembola: 
collophores. 



colla {K6X\a), glue; embolon {iix^oKov), a bolt, bar; — from their 



226 



AN INTRODUCTION TO ENTOMOLOGY 



of snow, where they appear as minute black specks, which spring 
away on either side from our feet as we walk; and some species 
collect in great numbers on the surface of standing water. Sev- 
eral species are known to be photogenic. 

The body consists of the head, three thoracic segments, and six 
abdominal segments (Fig. 230). The prothorax is usually small and 
in several genera is overlapped by the tergum of the mesothorax ; in 
theSminthuridffi the body-segrnents are more or less fused together. 
The structure of the abdomen is remarkable, as it consists of only six 
segments; there is no indication of the manner in which the reduc- 
tion of the number of segments has taken place. The anus is at the 
caudal end of the body; the genital opening is on a small papilla 
on the fifth abdominal segment. 

The antenna consist of from four to six segments, usually of four. 
They vary greatly in their comparative length; in some genera the 
last segment or the last two segments are divided into many rings 

orsubsegments(Fig.23o). 
The eyes of the Col- 
lembola are commonly 
described as a group of 
eight, or fewer, distinct 
simple eyes on each side 
of the head. But these 
so-called simple eyes are 
not ocelli; they are more 
or less degenerate omma- 
tidia, each group being 
the vestige of a com- 
pound eye. In Podura 
aquatica, these eyes, as 
figured by Willem ('00), 
are clearly ommatidia of 
the eucone type (Fig. 
231). In some other Col- 
lembola, as in Anurida 
niaritima (Fig. 232, O), 
the reduction of the om- 
matidia has progressed 
so far that they present 
the appearance of ocelli; and in still others the eyes are lost entire- 
ly. Primary ocelli have not been found in the Collembola. 

The mouth-parts are typically mandibulate; the jaws consisting 
of a pair each of mandibles, paragnatha, and maxillae. The parag- 
natha of Orchesella cincta were described by Folsom ('99) ; and those of 
Anurida niaritima by the same writer ('00). These organs were 
termed the siiperlingiiCB by Folsom. 

One of the most striking characteristics of the Collembola is that 
the jaws are apparently retracted into the cavity of the head so that 
only their tips are visible. But it has been shown by Folsom ('00), 




Fig. 232. — A, longitudinal section of an ommatid- 
ium and of the postantennal organ of Anurida 
niaritima; B, a surface view of the postantennal 
organ. (After Willem.) O, ommatidium ; Pa, post- 
antennal organ; hy, hypodemial cells; N, optic 
nerve; n, branch of the optic nerve; /, t, tuber- 
cles surrounding the postantennal organ;,, g, 
nerve-end-cell of the postantennal organ. (After 
Willem.) 



COLLEMBOLA 



227 




Fig. 233.— Hind foot of Ach- 
orutes maturus. (After Fol- 
som.) 



who studied the development of the mouth-parts of Anurida maritima, 
that, strictly speaking, the jaws are not "retracted," as is usually 
stated , but are overgrown by the genas. In an early embryonic stage, 
a downward projection of the gena ap- 
pears on each side of the head, and these 
"mouth -folds" become larger and larger 
in successive stages until the condition 
seen in the fully developed insect is 
reached. 

The development of mouth-folds is 
not restricted to the Collembola, but 
occurs also in the Entotrophous Thysan- 
ura, and to a less marked extent in many 
of the Pterygota, especially in some 
Orthoptera, where the gena of each side 
is prolonged into a small, but distinct, 
flat fold over the base of the mandible. 

In some of the Poduridas the mouth- 
parts are fitted for piercing and sucking, 
the mandibles and maxillae being styliform 
and projecting in a conspicuous cone. 

In some of the Collembola there is a 
sense organ situated between the base of the antenna and the ocular 
field; this is known as the postantennal organ; its presence o^ absence 
and its form when present afford characters used in the description 
of these insects. In its simplest form it is a claviform hyaline tubercle 
{Sminihurus) . A more complicated type is that of Anurida maritima, 
which has been figured by Willem ('00). In Figure 232, Pa repre- 
sents a longitudinal section of this organ. It is a nerve-end-cell, 
branching from the optic nerve and extending to the surface of the 
body, where it is covered by a very thin cuticular layer. It is pro- 
tected by a ring of tubercles {t, t), two of which are shown in the 
sectional view (A) and eight in the surface view (B). The function 
of this organ has not been determined; it has been suggested that it 
is an organ of smell. 

The legs of the Collembola consist each of five segments, which 
correspond to the five principal divisions of the legs of the higher 
insects. Willem ('00) considers the two antecoxal pieces as segments 
of the legs and consequently states that the legs are composed of 
seven segments The tarsi in most genera bear two claws, an outer, 
larger one, the unguis, and an inner, smaller one, the unguiadus; these 
claws are apposable (Fig. 22,^); in some genera the inner claw is 
wanting. 

One of the most characteristic features of the Collembola is the 
collophore, or ventral tube, which is situated on the ventral aspect of 
the first abdominal segment (Fig. 230, co). This organ varies greatly 
in form in the different genera; in some it is a simple tubercle, di- 
vided into two halves by a central slit; in others it is enlarged and 
becomes a jointed tube divided at its free end into two lobes. The 



228 



AN INTRODUCTION TO ENTOMOLOGY 



collophore bears at its extremity a pair of eversible sacs through the 
walls of which exude a viscid fluid. By means of this organ these 
insects are enabled to cling to the lower surface of smooth objects. 
The collophore is developed from a pair of appendages, which in the 
course of their development become fused together at their base. 

The third abdominal segment usually bears a pair of short append- 
ages, whose basal segments are fused; this is the tenaculum, or catch 
(Fig. 230, c), which holds thespring when it is folded under the abdomen. 

The spring or furcula (Fig. 230, s) is formed by the 
appendages of the fourth abdominal segment which are 
united at the base but separate distally. These ap- 
pendages are three-jointed. The united basal seg- 
ment is termed the manubrium (Fig. 234, ma); the 
intermediate segments, the denies (Fig. 234, d); and 
the terminal segments, the mucrones (Fig. 234, mu). 

In the Entomobryidse the furcula appears to be 
formed by the appendages of the fifth abdominal seg- 
ment; but a study of the muscles that move it shows 
that it really pertains to the fourth segment. In some 
genera of the Podurid^ the furcula is wanting. 

The order Collembola includes two quite distinct 
types of insects; in one of these types the body is 
elongate w4th distinct segmentation; in the other 
the body is shortened, the abdomen globose and its 
segments in part fused. Based on this distinction the 
order is divided into two suborders as follows : 




Fig. 234.— The 
furcula of Pa- 
pirius: ma, 
manubrium; 
d, left dens; 
mil, left muc- 
ro. (After 
Lubbock,) 

A. Body elongate Suborder Arthropleona. 

AA. Body globose Suborder Symphypleona. 




Fig. 235. — The rnow- 
flea, A chorutes ni'vi- 
cola. (After Fol- 
som.) 



Suborder I. ARTHROPLEONA* 

Body elongate with distinct segmentation, rare- 
ly with the last two or three segments of abdomen 
partially fused; tracheae absent. 

Family i, Poduridae. Furcula, when pres- 
ent, clearly appended to the fourth abdominal 
segment; prothorax well developed; cuticula 
usually granulated. 

Among the better-known members of this 
family are the following: The "Snow -flea," 
Achoriites nivicola, which occurs abundantly in 
winter on the surface of snow (Fig. 235); this 
species is also known as Achoriites socidlis. 
Achoriites armdtus is often found on fungi. 



*Arthropleona : arthron (dpdov), 
stacean's abdomen. 



joint; pleon, a cru- 



SYMPHYPLEONA 229 

Anurida marUima occurs abundantly on the seashore, chiefly between 
tide marks; several important embryological and anatomical mono- 
graphs have been published regarding this species. Podiira aqiiatica 
is one of the most abundant members of the Collembola; it occurs 
on the surface of standing water on the margins of ponds and streams. 

Family 2, Entomobryidae. Furcula present and apparently 
appended to the fifth abdominal segment; prothorax reduced and 
cuticula not granulated. 

This is the largest family of the Collembola, containing many 
genera and species. In some genera the body is clothed with scales. 
To this family belongs the genus Orchesella, the only genus in the 
Collembola in which the antennae consist of six segments. 



Suborder II. SYMPHYPLEONA* 

Body shortened, sitbglobniar in shape with segments of body, except 
the last two, fused closely together and segmentation mostly obliterated; 
trachecB present in some genera. 

Family 3, Neelidae. Antennae short 
and stout; thorax large and longer than 
abdomen. The principal genera are 
Neehis and Ne elides. 

Family 4, Sminthuridae. Antennse 
long and slender; thorax shorter than 
abdomen. The principal genera Smin- 
thurus and Papirius. 

In Sminthurns, trachea are present; in Fig. 236. — Papirius fuscus- 
the other genera they are absent or ex- (After Lubbock.) 
tremely vestigial. The presence of tra- 
cheae in Sminthurns enables these insects to live in drier situations 
than can other Collembola. The " garden-^ea" S^mnthiirus hortensis 
is found upon the leaves of young cabbage, turnip, cucumber, and 
various other plants. 

*Symphypleona ; symphyo, to grow together; pleon, a crustacean's ab- 
domen. 



%g^ 

/^l^^^^ 



Subclass II. PTERYGOTA 

Winged Insects 

The members of this subclass are winged; or, if without wings, they 
have had winged ancestors and this is an acquired condition. The 
mouthparts vary; in some they are sucking, in others chewing. The 
metamorphosis varies from slight to gradual to complete. 

Much the greater number of species of insects belong to this 
subclass and much the greater number of them possess wings, for 
example, the beetles, flies, wasps, bees, and many others. Many 
aphids, all fleas, lice, worker ants, female scale insects, and some 
others have no wings. The wingless condition of these forms, how- 
ever, is an acquired one, for the evidence is clear that they have de- 
scended from winged ancestors. The subclass Pterygota contains all 
of the remaining twenty -three orders discussed in this book. 



CHAPTER Vlir 
ORDER ORTHOPTERA* 

Grasshoppers, Crickets, Cockroaches, and others 

The winged members of this order have two pairs of wings; the fore 
wings are more or less thickened, hut have a distinct venation; the hind 
wings are folded in plaits like a fan when at rest; there are many forms 
in which the wings are vestigial or even wanting. The month-parts are 
formed for chewing. The metamorphosis is gradual (paurometabolous) ; 
the nymphs are terrestrial. 

The order Orthoptera includes some of the veiy common and best- 
known insects. The most famiHar representatives are the long-homed 
grasshoppers, locusts, crickets, katydids, and cockroaches. 

With the exception of a single family, the Mantidae, the members 
of this order are as a rule injurious to vegetation; and many species 
are quite apt to multiply to such an extent that their destruction of 
plant life becomes of great economic importance. 

The two pairs of wings of the Orthoptera differ in structure. 
The front wings are leathery or parchment-like, forming covers for 
the more delicate hind wings. These wing-covers have received the 
special name tegmina. The tegmina usually overlap, at least at the 
tips, when at rest. The hind wings are thinner than the tegmina and 
usually have a broadly expanded anal area, which is folded in plaits 
like a fan when at rest. Many Orthoptera have vestigial wings, and 
many are wingless. In the males of the Saltatorial Orthoptera, the 
Locustidse, the Tettigoniidae, and the Gryllidae, musical organs have 
been formed by modifications of certain parts of the wings; these 
have been described in Chapter II. 

The mouth-parts are of the mandibulate type, that is, they are 
formed for chewing. The mouth-parts of a locust are figured on 
page 42. 

In the Orthoptera the metamorphosis is gradual, paurometabo- 
lous. In the case of those species in which the wings of the adult are 
either vestigial or wanting, the adults resemble very greatly immature 
insects. It is often important to determine whether a short-winged 
specimen is an adult or not. Fortunately this determination can 
usually be made with ease with the Saltatorial Orthoptera, the 
Locustidae, the Tettigoniidae, and the Gryllidae. In these three families 
the wing-pads of the nymphs are inverted, as shown by the curving 
down of the extremities of the wing-veins, instead of up as with the 
adult; and the rudimentary hind-wings are outside of the tegmina, 
instead of beneath them. The development of the wings of a locust 
is described in Chapter IV, p. 175. 

*0rth6ptera: orthos (dpdos), straight; pteron {irrepbv), a wing. 
(230) 



ORTHOPTERA 



23 i 




The segmentation of the abdomen and the development and 
structure of tlie genitaha or gonapophyses in the jumping Orthoptera 
are of especial interest; as, on account of the generalized condition 
of these parts in these insects, they can serve as a type with which the 
corresponding parts in more specialized insects can be compared. In 
some members of this group of families all of the abdominal segments 
are preserved more or less distinct, and in nearh^ all of them the 
genitalia are well-developed.* 

The segmentation of 
the abdomen can be seen 
best on the dorsal aspect 
of this region; for in 
some cases the tergiun of 
a segment is well-pre- 
served while the sternum Fig. 237. — Side view of a locust with the wings re- 
is vestigial. Figure 237 moved: /, tympanum. 

represents a side view of a female locust with the wings removed in 
order to show the segmentation of the abdomen. The first eight 
segments of the abdomen of this insect are very distinct; but the 
caudal segments are much less so. Figure 238 represents the caudal 
part of the abdomen of the same insect more enlarged, in order to 

. _ facilitate the lettering of the parts. 

In this insect the eighth abdominal 
tergum resembles the preceding ones. 
The ninth and tenth abdominal terga 
are shorter and are joined together on 
each side; but in many other jumping 
Orthoptera these terga are not thus 
o..^^\ \ \JLy united. Caudad of the tenth abdomi- 
nal tergum there is a shield-shaped part, 
which is commonly known as the 
Fig. 238.- Side view of the caudal supra-anal plate; this plate is divided 
end of the abdomen of a female into two sclerites by a transverse su- 
ture; the first of these sclerites is be- 
lieved to be the tergum of the eleventh 
abdominal segment, and the other the 
telson (Fig. 238, t). Thus all of the 
abdominal segments are preserved, in 
part at least, in this insect. 




locust: 8, p, 10, II, the tergites 
of the eighth, ninth, tenth, and 
eleventh abdominal segments; /, 
telson; p^ podical plate; c, cer- 
cus; d, i, V, dorsal, inner, and 
ventral valves of the oviposi- 
tor. 



The last two abdominal segments, the eleventh and the telson, are 
even more distinctly preserved in the early instars of some orthopterous 
insects than they are in the adult (Fig. 239). In many adult Orthop- 
tera there is no suture between the eleventh tergum and the telson. 

On each side of the body, in the angle between the supra-anal 
plate and the lateral part of the tenth tergum, there is a 
triangular sclerite (Fig. 238, p); this pair of sclerites has long been 



*The genitalia are vestigial in Tridaclylus and are entirely wanting in Gryllo- 
talpa. In these genera the reduction or loss of the genitaliu is probably correlated 
with the subterranean life of these insects, they having no need for an ovi]:ositor. 



232 



AN INTRODUCTION TO ENTOMOLOGY 




known as the podical plates; but they have recently been named 
the para prods because they are situated one on each side of the 
anus. They are the sternum of the 
eleventh abdominal segment, which 
is divided on the midventral line, to 
admit of the expansion of the poste- 
rior end of the alimentan,' canal during 
defecation. 

In this insect the cerci (Fig. 238, c) 
project from beneath the caudal border 
of the tenth tergum ; they appear, there- 
fore, to be appendages of the tenth ab- 
dominal segment; but it is believed 
that in all insects where cerci are pres- 
ent they are appendages of the elev- 
enth abdominal segment. This, for 
example, is obviously the case in the 
Plecoptera (Fig. 240). The homology 
Fig. 239.-Caudal segments of a o^ the paraprocts IS also well shown in 
nymph of a female locust, dorsal this figure. 

aspect: 11, eleventh abdominal 'phg ovipositor consists of three 

segment; /, telson; r, cercus. ^^^-^^ ^^ processes or gonapophyses ; 
these are termed the valves or valvula of the ovipositor; they are dis- 
tinguished as the dorsal, ventral, and inner valvulae, respectively. 
In the locust the dorsal valvulae (Fig. 238, <i) and the ventral valvulce 
(Fig. 238, v) are strong, curved, and pointed pieces; the inner valvu- 
lae (Fig. 238, i) are much smaller. 

The relation of the gonapophyses to the segments of the abdomen 
can be seen more clearly in the female of Ceuthophilus- (Fig. 241). 
The ventral valvulae arise from the posterior margin of the eighth 
stemimi and the dorsal and inner valvulce arise from the ninth 
sternum. These relations can be seen even more clearly in very young 
nymphs where the rudiments of the gonapophyses are mere tubercles, 
one pair on the hind margin of the 
eighth abdominal stemiun and two 
pairs on the ninth sternum (Fig. 
242). 

In the male, as in the female, 
the form of the caudal end of the 
abdomen and its appendages dif- 
fers greatly in different members of 
this order. Space can be taken here 
to illustrate these parts in only a 
single species. For detailed ac- 
counts of these parts in other mem- Fig. 240.— End of abdomen of Pier- 
bers of this order, special papers on onarcys dorsata, female, ventral 

this subject should be consulted. ""f^T- V- ^'l^^^t/''^^^^^ ^tevnnm 

, .1 ,1 of the eleventh abdominal segment. 

Among the more recent and gen- the podical plates; c, c, basal parts 

erally available of these are those of of the cerci. 




ORTHOPTERA 



233 



Crampton ('i8) and Walker ('19 and '22 b). These papers include 
references to the very CAtended literature on this subject. 

Figures 243 and 244 represent the caudal end of the abdomen 
of the male of the Carolina locust, Dissosteira Carolina. In this 
insect the ninth and tenth terga are joined together on each side 
(Fig. 244) and the eleventh tergum is separated from the apical 
part of the supra-anal plate (Fig. 243, s) by a distinct suture. The 
ninth sternum is large, is turned upward behind, and bears a large con- 
ical part (Fig. 244, ex) termed the coxale, which is believed to be 
united coxites of the ninth segment. 

There are two genera of rare and remarkable insects, each of which 
has been placed in the Orthoptera by some writers and each of which 




Fig. 242. — Ventral 
view of end of 
abdomen of 

Fig. 241.— Side view of end of abdomen of Ceiithophilvs yonng nymph of 
lapidicola: 7, 8, 9, 10, above, tergites of the seventh Conocephalusfas- 
to the tenth abdominal segments; 7, 8, below, sternites w'^ft'^' ^-^^^^^ 
of the seventh and eighth abdominal segments; b, basal Walker.) 
segment of the ventral valve of the ovipositor; c, cercus; 
p, podical plate; d,i, v, dorsal, inner, and ventral valves 
of the ovipositor. (After Walker.) 

is regarded by others as constituting a separate order; these are 
Grylloblatta and Hemimerus. These genera are briefly discussed at 
the close of this chapter. 

Leaving out of account the two genera named above, the order 
Orthoptera includes only six families, all of which are represented in 
the United States. These families can be separated by the following 
table.* 

TABLE OF FAMILIES OF ORTHOPTERA 

A. Hind femora fitted for jumping, i. e., very much stouter or very much longer, 
or both stouter and longer, than the middle femora; organs of flight of imma- 
ture forms inverted; stridulating insects. (The Saltatorial Orthoptera.) 



*The limits assigned to the order Orthoptera in this work are those that have 
been commonly recognized for a long period and are those adopted in recently 
published manuals treating of this order, except that in some of them the Der- 
maptera is included in the Orthoptera. But Handlirsch ('o8j in his great work on 
fossil insects proposed a new classification of insects, which differs greatly from 
the classification adopted here. In this classification the families Blattidae, 
Mantidse, and Phasmidae are removed from the Orthoptera and each is made to 
constitute a distinct order. 



234 



AN INTRODUCTION TO ENTOMOLOGY 



B. Antennae long and setaceous, except in the mole-crickets and sand-crickets; 

tarsi three- or four-jointed; organs of hearing situated in the fore tibis; 

ovipositor elongate, except in the mole-crickets and sand-crickets, with its 

parts compact. 

C. Tarsi four-jointed; ovipositor, when exserted, forming a strongly- 
compressed, generally sword-shaped blade, p. 234 Tettigoniid^ 

CC. Tarsi usually three-jointed, except in the pigmy mole-crickets where 
they are reduced; ovipositor, when exserted, forming a nearly cylindrical, 
straight, or occasionally upcurved needle, except in the Trigonidiinas. 

p. 242 Gryllid^. 

BB. Antennse short; tarsi three-jointed; organs of hearing situated in the 
first abdominal segment; ovipositor short, with its parts separate. 

p. 252 LoCUSTIDiE 

AA. Hind femora closely resembling those of the other legs, and scarcely if at 
all stouter or longer than the other femora, i. e., not fitted for jumping; 
organs of flight. in a normal position when immature; stridulating organs 
not developed. 
B. Body elongate; head free; pronotum elongate; legs slender, rounded; 
cerci jointed or without joints; walking insects. 

C. Front legs simple; cerci without joints, p. 260 Phasmid^e 

CC. Front legs fitted for grasping; cerci jointed, p. 262. . .Mantid/E 

BB. Body oval, depressed; head wholly or almost wholly withdrawn beneath 

the pronotum; pronotum shield-like, transverse; legs compressed; cerci 

jointed; rapidly running insects, p. 263 Blattid^e 




Fig. 243. — Dorsal view of end 
of abdomen of Dissosteim 
Carolina, male: qT, ioT, 
iiT, ninth, tenth, and elev- 
enth terga; s, supra-anal 
plate; py podical plate, c, 
cercus; ex, coxale. 




Fig. 244. — Side view of end of abdomen 
of Dissosteira Carolina, male; lettering as in 
Figure 243. 



FAMILY TETTIGONIID^ 

The Locustidae of Authors* 

The Long-horned Grasshoppers 

To this family belong the most attractive in appearance of our 
common Orthoptera. In many of them the wings are graceful in 

*The name Locustidag has been commonly applied to this family. This usage 
is the result of an erroneous application of the generic name Loctista to certain 
members of this family. The insects of the genus Locusta, established by_ Lin- 
naeus, and other insects commonly known as locusts, are members of the family to 
which the common name short-horned grasshoppers is applied and which is 
properly termed the Locustidce. 

The Tettigoniidae is the Phasgonurida; of Kirby's catalogue. 



ORTHOPTERA 235 

form and delicate in color, and the antennae are exceedingly long and 
slender, looking more like ornaments than like organs of practical use. 
These beautiful creatures are much less frequently seen than are 
the crickets and locusts because of their protective green color, which 
renders them inconspicuous in their haunts among foliage or on the 
blades of grass. Their presence is most often indicated by the chirping 
of the males. 

The long-homed grasshoppers are those jumping Orthoptera with 
long, slender antennge, longer than the body, in which the tarsi are 
four-jointed and the ovipositor is sword-shaped. 

The tegmina of the males are furnished, in nearly all winged 
species, with stridulating organs; but these occupy a much smaller 
part of the tegmina than with the crickets. The six plates of which 
the ovipositor is composed are closely united so that this organ has 
the appearance of a single sword-shaped blade. 

The different members of the TettigoniidcC exhibit a great variety 
of methods of oviposition; some lay their eggs in the ground; some 
in the pith of twigs ; some singly in the edges of leaves ; some in rows 
on leaves and stems; and others between the root -leaves and stems 
of various plants. 

The Tettigoniidce found in America north of Mexico represent 
eight subfamilies; these can be separated by the following table, 
which is based on one by Scudder ('97). 
A. Body generally winged; tarsi more or less depressed. 

B. Fore tibiag furnished with auditory tympana; fore wings of male, when 
present, furnished with stridulating organs. 

C. First two segments of the tarsi without a lateral groove; the two series of 
spines on the hind side of the posterior tibiee continued to the apex. p. 236. 

Phaneropterin^ 
CC. First two segments of the tarsi with a lateral groove; one or both of 
the two series of spines on the hind side of the posterior tibias not con- 
tinued to the apex. 
D. Fore tibiae without apical spines above. 

E. The apex of the vertex short, crowded by the prominent antennary 
fossse; pronotum crossed by two distinct sutures, p. 238 

PsEUDOPHYLLINiE 

EE. The apex of the vertex extended and free from the not prominent 

antennary fossae; pronotum without transverse sutures, or with 

only one. 

F. Fore and middle femora unarmed beneath ; the vertex terminating 

in a rounded tubercle, which is hollowed out on the sides, p. 238. 

CONOCEPHALIN^ 

FF. Fore and middle femora spined beneath, the vertex produced 

forward into a long sharp cone. p. 239 Copiphorin^ 

DD. Fore tibiae with an apical spine above on the outer side; usually 

wingless or with vestigial wings, p. 239 Decticin^ 

BB. Fore tibias without auditory tympana; fore wings of male, when present, 

without stridulating organs, p. 240 Gryllacrin^ 

AA. Body usually wingless; tarsi distinctly compressed. 

B. Tarsi without pulvilli; inserting angle of the hind femora situated on the 

inner side. p. 241 Rhaphidophorin^ 

BB. Tarsi provided with pulvilli; inserting angle of the hind femora situated 
on the outer side. p. 242 Stenopelmatin.« 

Some of the more common and better-known representatives of 
these families are referred to below. To save space the distinguishing 



236 



AN INTRODUCTION TO ENTOMOLOGY 



characteristics of the subfamilies are not repeated ; these are indicated 
in the table above. 

Subfamily PHANEROPTERIN^ 

The False Katydids 




To this subfamily belong certain long-horned grasshoppers that 
have broad leaf -like wings and arboreal habits. In these respects 
they resemble the well- 
known katydid w^hose stri- 
dent call suggested the pop- 
ular name. Several of these 
species have received popu- 
lar names in which the word 
katydid enters, as indicat- 
ed below. These species 
may be termed collectively 
the false katydids ; the true 

katvdids constitute the next 77;„ ^./^ a ui >,? uj -f t ^t? ^ 
.-. .. rig. 246. — Amblycoryphaobiongtfolia. (From 

subfamily. Lugger.) ^ ^'^ *■' 

Blatchley ('20) describes twenty species and varieties of the false 
katydids that are found in northeastern America; these represent 
eight genera. Among our common species there are representatives 
of three genera; these can be separated as follows. 

A. Tegmina broadened in the middle; the extreme point of the vertex much 
broader than the first segment of the antennas. 




ORTHOPTERA 



237 




—Scudderia septentr 
(From Lugger.) 



B, Hind femora much shorter than the tegmina; ovipositor short and turned 

abruptly upward (Fig. 245). p. 237 Microcentrlim 

BB. Hind femora but Httle if any shorter than the tegmina; ovipositor well 

developed, and curved gradually upward, p. 237 Amblycorypha 

AA. Tegmina of nearly equal breadth throughout; the extreme point of the 
vertex but little if any broader than the first segment of the antennae, p. 237. 

Scudderia 

Microcentmm. — Two species of this genus are found in the United 
States east of the Rocky Mountains; these are known as the angular- 
winged katydids. Figure 245 repre- 
sents the female of the larger angular- 
winged katydid, Microcentmm rhombi- 
folium, and the remarkable way in 
which it deposits its eggs on leaves and 
twigs. In this species the slightly hol- 
lowed front of the pronotum has a very 
small central tooth, which is lacking in 
smaller species. The smaller angular- 
winged katydid, Microcentrum retinerve, is only slightly smaller than 
the larger one. 

Amblycorypha. — The three most common species of the genus 
are the following: The oblong-winged katydid, Amblycorypha oblongi- 
Jolia (Fig. 246), is the largest of the 
three most common species. The 
tegmina measure from 34 to 37 mm. 
in length; the ovipositor is less ser- 
rate and less curved than in the next 
species. The round-winged katydid, 
Amblycorypha roHmdifdlia, is a smaller 
species ; the tegmina are not more than 
30 mm. in length and are wnde for their 
length, as indicated by the specific 
name; the ovipositor is quite broad, 
much curved, and roughly serrated. 
Uhler's katydid, Amblycorypha tihleri, 
is our smallest species; the body meas- 
ures from 14 to 16 mm. in length; the 
tegmina from 24 to 26 mm.; and the 
ovipositor about 8 mm. 

Scudderia. — Species of this genus 
are found throughout the United 
States and in Canada; but the greater 
number of our species are found east 
of the Great Plains. One species, 
Scudderia mexicdna, is found in Cali- 
fornia and Oregon. A common eastern 
species which may serve as an ex- 
am-ple of the insects of this genus, is 
the northern bush-katydid, Scudderia 
septentriondlis. Figure 247 represents 




Pterophvlla caniellifo- 
(After Harris.) 



the male of this species, natural size. 



238 



AN INTRODUCTION TO ENTOMOLOGY 



Subfamily PSEUDOPHYLLIN^ 
The True Katydids 

The best -known representative of this subfamily in the United 
States is the northern true katydid, Pterophylla camellijolia (Fig. 
248). This insect is found throughout the United States east of 
the Rocky Mountains; but in the North it Hves in colonies which 
occupy quite limited areas. This is the insect whose song suggested 
the popular name katydid. It differs from members of the preceding 
subfamily in having the hind wings shorter than the tegmina, and in 
having the tegmina very convex, so that it has an inflated appearance. 
Subfamily CONOCEPHALIN^. 
The Meadow Grasshoppers 

From the middle of the summer to the autumn there can be found 
upon the grass in our meadows and moist pastures many light-green 
long-horned grasshoppers of 
various sizes; these, on ac- 
count of the situations in 
which they are usually found, 
are termed the meadow- grass- 
hoppers. Our common species 
represent only two genera ; but 
each of these includes many 
species. 

Orchelimum. — This genus 
includes the larger and stouter 

species of meadow grasshoppers; but they are of medium size com- 
pared with other Tettigoniidae. In these the ovipositor is usually 




Fig. 249. — Orchelimum vulgare, mal; 
(Prom Lugger.) 





Fig. 251. — CoiiocephalHs 



Fig. 250. — Orchelimum vulgare, female. 
(From Lugger.) 
up-curved. Our most abundant species is the common meadow 
grasshopper, Orchelimum vulgare. This is found from the Rocky 
Mountains to the Atlantic Coast. Figure 249 represents the male, 
natural size; and Figure 250, the female. 

Conocephalns.— This genus comprises the smaller and slenderer- 
species of this subfamily. In these the ovipositor is slender, and 
straight or slightly curved (Fig. 251). Until recently this genus has 
been generally known as Xiphidium.* 

*It is unfortunate that according to the rules of nomenclature the name 
Conocephalus must be applied to this genus instead of to the typical genus of the 
next subfamily, now known as Nsoconocephalus, with the result that the sub- 
family name ConocephaUnje is applied to the meadow grasshoppers instead of to 
the cone-headed grasshoppers. 



ORTHOPTERA 
Subfamily COPIPHORIN.E 



239 



The Cone-headed Grasshoppers 

The cone-headed grasshoppers are so called because the vertex is 
prolonged forward and upward into a cone. These are much larger 
insects than the meadow grass- 
hoppers and are found in trees as 
well as upon grass. This sub- 
family is represented in our fauna 
by four genera; but three of 
these are found only in the South. 
All of the northern species belong 
to the genus Neoconocephaltis, of 
which eleven species occur in the 
United States. The most com- 
mon species in the north, east of 




Fig. 252. — Neoconocephaltis ensiger, 
male. (From Lugger.) 



the Rocky Mountains, is the sword-bearer, Neoconocephalus ensiger. 
Figure 252 represents the male of this species, and Figure 253 the 
female. Both sexes have very long wings, and the ovipositor of the 
female is remarkable for its length. 




Fig. 253. — Neoconocephalus ensiger, female. (From Lugger.) 

In most of the species of Neoconocephalus there are two distinct 
forms : one pea-green in color and the other of a brownish straw-color. 



Subfamily DECTICINiE 



The Shield-backed Grasshoppers 

A few members of this subfamily have well-developed wings ; but 
in most species the wings are small, especially in the female, where 
they are sometimes even absent. Most of the species bear some 
resemblance to crickets. They present, however, a strange appear- 
ance, due to the pronotum extending backward over the rest of the 
thorax, like a sun-bonnet worn over the shoulders with the 



240 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. 254. — Atlantictis testacens, 
(From Lugger.) 



male. 



back side forward. It was the large size of the pronotum that sug- 
gested for the group the popular 
name the shield-hacked grass- 
hoppers. 

These insects live in grassy 
fields or in open woods, where 
they hop about in exposed posi- 
tions. Even in some of the short- 
winged forms the stridulating or- 
gans of the tegmina of the males 
are well deiveloped. 

The North American species 

represent twenty genera ; most of 

these are found west of the Mississippi River, a few species occur m 

the east; nearly all of these belong to the germs A tldnticus. Figure 

254 represents the male of At- 
IdnticMS testdceus, and Figure 

255 the female of Atlanticus 
davisi. 

Most of the species of this 
subfamily are local or very 
rare and not of economic im- 
portance; but species of the 
genus Anabrus and of Perana- 
brus at times invade cultivated areas in the western United States 
and do immense damage. Many popular names have been applied 
to these insects; perhaps the one in most general use is the western 
cricket. 

A very complete monograph of the North American species of 
this subfamily has been pubHshed by Caudell ('07). 




Fig. 255. — A tlanticus davisi, female. 



Subfamily GRYLLACRIN.^ 



The Leaf -rolling Grasshoppers 

The members of this subfamily agree with the preceding sub- 
families and differ from the two following in having the tarsi more or 

less depressed. They 
agree with the fol- 
lowing subfamilies 
and differ from the 
preceding in the ab- 
sence of auditory 
t>Tnpana in the fore 
tibias and in the ab- 
sence of stridulating 
organs even when the 
tegmina are present. 
Only a single spe- 




Fig. 256. — Camptonotus carolinensis, female. 
Blatchley.) 



(From 



ORTHOPTERA 



241 



cies, the Carolina leaf-roller, Camptondtus carolinensis (Fig. 256), 
occurs in our fauna. This species is wingless; it measures from 
13 mm. to 15 mm. in length. Its known range extends from New- 
Jersey west to Indiana and south to Florida. 

This insect is very remarkable in its habits,which have been de- 
scribed by Caudell ('04) and McAfee ('08). It makes a nest by 
rolling a leaf and fastening the roll with silken threads which it 
spins from its mouth. It remains in its nest during the day and 
emerges at night to capture aphids upon which it feeds. 



Subfamily RHAPHIDOPHORIN^ 

The Cave-Crickets or Camel-Crickets 

Many common names have been applied to members of this sub- 
family; SLxnong these are cave-crickets, because they abound in caves 

and are found in other 
dark places; camel-crick- 
ets, because of the high, 
arched back of some 
species (Fig. 257); and 
stone-crickets, from their 
habit of hiding beneath 
stones. This last name 
is not at all distinctive. 
These are wingless 
long-horned grass- 
hoppers that bear some 
resemblance to the true 
crickets (Fig. 258). They have a short, thick body and remark- 
ably stout hind femora, like a cricket, but are entirely destitute 
of tegmina and wings, and the females, like other Tettigoniidse, have 
a sword-shaped ovipositor. The more common species are either of 
a pale brown or a dirty white color and more or less mottled with 
either lighter or darker shades. 




Fig. 257. — Ceuthophilus uhleri, male. (From 
Blatchley.) 





Fig. 258. — Ceuthophilus, female. 



Fig. 259. — Ceuthophilus niaculatus, 
female. (From Lugger.) 



These insects live in dark and moist places, under stones and 
rubbish, especially in woods, in cellars, in the walls of wells, and 
in caves. On one occasion I saw many thousands of them on the 
:oof of a cave in Texas. 

Caudell ('16) in his monograph of this subfamily lists twelve gen- 
era including many species that occur in the United States. Most of 




242 AN INTRODUCTION TO ENTOMOLOGY 

our common species in the East belong to the genus Ceuthophilus. 
Figure 257 represents themale oi Ceuthophilus uhleri, and Figure 2 i,g 
the female of Ceuthophilus maculdtus. 

Subfamily STENOPELMATIN^ 

The Sand-Crickets 



These are large, clumsy- 
creatures with big heads (Fig. 
260). They live under stones 
and in loose soil. They are 
represented in our fauna by 
a single genus, Stenopelmatus, 
several species of which are 

found in the Far West and pjg. 260. -Stenopelmatus. 

especially on the Pacmc Coast. 

Family GRYLLIDAE* 
The Crickets 

Although the word cricket forms a part of some popular com- 
pound names of members of the Tettigoniidee, as "western crickets" 
and "sand-crickets," when the word is used alone it is correctly ap- 
plied only to members of this family. 

In the more typical crickets, the hind legs are fitted for leaping; 
the antennas are long and slender; the tegmina lie flat on the back 
and are bent down abruptly at the sides of the body; the ovipositor 
is spear-shaped; and the tarsi are three-jointed. Wingless forms are 
common. 

The more striking departures from these characteristics are the 
following: in the Tridactylinae the antennas are short; in the Tri- 
gonidiinas the ovipositor is sword-shaped; in the Gryllotalpinas and 
the Tridactylinae the ovipositor is wanting in our species; and in 
the Tridactylinas the tarsi are reduced. 

It is evident that one step in the reduction of the nimiber of tarsal 
segments is the growing together of the metatarsus and the second 
segment. This is shown in the hind tarsi of Anaxlpha, CEcdnthus, 
Nemohius, and doubtless others, where the suture between these two 
segments can be seen although the segments are anchylosed. 

Tjonpana are usually present in the fore tibiae, one on each side 
of each tibia, as in the Tettigoniidce. In some genera one tjinpanimi 
of each pair is wanting ; this is sometimes the outer and sometimes the 
inner one; in the wingless, and therefore mute, species, the tympana 
are wanting; and in the Tridactylince there are none. 



*This family is termed the Achetidae by some writers. 



ORTHOPTERA 243 

With most species of crickets the two sexes differ greatly in ap- 
pearance; the female has a long ovipositor and the venation of the 
wings is simple, while the male has the horizontal part of the fore 
wings modified to form musical organs. The structure of these has 
been described in Chapter 11. 

The Gryllidse includes eight subfamilies, all of which are repre- 
sented in the United States. These subfamilies can be separated by 
the following table. 

A. The next to the last segment of the tarsi distinct, depressed, and heart- 
shaped. 
B. Hind tibiae armed with two series of spines without teeth between them. 

p. 243 Trigonidiin^ 

BB. Hind tibiae with teeth between the spines, p. 244 Eneopterin^ 

AA. Tarsi compressed, the next to the last segment minute, compressed. 
B. Fore legs fitted for walking. 

C. Hind tibiae without spines except the apical spurs. 

D. With well-developed wings; hind tibias with only two very small 

apical spurs. (Neoxabea.) p. 245 QJcanthin^ 

DD. Wingless or subapterous; hind tibias with three pairs of apical 

spurs, p. 250 MOGOPLISTIN^ 

CC. Hind tibiae armed with two series of spines. 

D. Body subspherical ; wingless; hind femora ovate, very strongly 

swollen, p. 249 Myrmecophilin^ 

DD. Body more elongate, usually winged; hind femora more elongate, 
not exceptionally swollen. 
E. Hind tibiae with minute teeth between the spines, p. 245 CEcanthin^ 

EE. Hind tibiae without teeth between the spines, p. 247 Gryllin^ 

BB. Fore legs fitted for digging. 

C. Antennae many-jointed ; all of the tarsi three-jointed, p. 250 

Gryllotalpin^ 

CC. Antennae el even- jointed; fore and middle tarsi two-jointed, hind tarsi 
one-jointed or wanting, p. 251 Tridactylin^ 

Subfamily TRIGONIDIIN^ 
The Sword-bearing Crickets 

These are small crickets, our species measuring from 4 mm. to 
8.5 mm. in length of body. They live chiefly on shrubs and tall 
grasses and weeds growing in or near water. Their distinguishing 
features are the following : The next to the last segment of the tarsi 
is distinct, depressed, and heart-shaped, the hind tibias are slender 
with three pairs of mobile spines besides the terminal spurs, and 
with no teeth between these spines; and the ovipositor of the female 
is compressed and curved upwards. In the sword-shaped form of the 
ovipositor these crickets present a striking exception to the character- 
istics of the Gryllidas. 

The following are our best-known representatives of this sub- 
family. 

Anaxtpha extgua.— This cricket resembles somewhat in general 
appearance the common small field-crickets (Nemobius), but unlike 



244 



AN INTRODUCTION TO ENTOMOLOGY 



them it does not live on the ground. The antennae are very long 
(Fig. 261); the ovipositor is one half as long as 
the hind femora; the hind femora of the male 
are longer than the tegmina; and the stridu- 
lating area of the tegmina is large. The length of 
the body is 5-8 mm. 

There are two forms of this species: in one, 
the hind wings are wanting and only the tympana 
on the outer face of the fore tibise are present ; in 
the other, long hind wings are present and there 
is a tympanum on each face of the fore tibiae. 
This species is found from southern New 
England west to Minnesota and Nebraska and 
south to Florida and Texas. 

Falctcula hebdrdi. — This is a smaller species 
than the preceding, the body measuring only 4-5 
mm. in length. It is uniform pale yellowish brown 
in color. The hind wings are wanting. The 
stridulating area is small, confined to the basal 
fourth of the tegmina. The fore tibiae are without 
visible t^Tnpana. Its range extends from New 
Jersey south and southwest to Florida and Texas. 
Cyrtoxipha colmnbidna. — This is a small, pale 
green fading to brownish yellow, cricket; it is 
found on shrubs and small trees, usually near 
water. The wings are always present and pro- 
longed in the form of a tail or queue. Tjonpana 
are present on both faces of the fore tibiae. The 
tegmina extend 2-3 mm. beyond the end of the 
abdomen. The length of the body to apices of 
Fig. 26i.--^jwA:i^/m ^gjyjnina is 8.^ mm. Its range extends from 
extgua. (From Lug- Washington. D. C, to Florida and Texas. 

Phylloscyrtus pulchellus. — This cricket differs 
from the three preceding species in having the last segment of the 
maxillary palpi spoon-shaped. The head and the thorax are bright 
crimson-red; the margin of the thorax is pale yellow; the abdomen 
is black, and the tegmina are chestnut-brown. The length of the 
body is 6-7 mm. This species is found throughout the United States 
east of the Mississippi River, except in the northern portions. 



Subfamily ENEOPTERIN^ 
The Larger Brown Bush-Crickets 



These crickets resemble those of the preceding subfamily in the 
heart-shaped form of the next to the last segment of the tarsi ; but 
differ in having teeth between the spines of the tibise, and in the 
ovipositor being spear-shaped. 



ORTHOPTERA 



245 



These represent 




Only a few species are found in our fauna, 
three genera: Orocharis, in which both t^in- 
pana of the fore tibiae are present ; Hdpithus, with 
a tympanum on the inner face only of the fore 
tibiae; and Tafaltsca, with no tympana and no 
stridulating organs. 

The most common species is Orocharis saltdtor 
(Fig. 262). This is usually pale reddish brown, 
but some individuals are grayish. The length 
of the body is 14-16 mm. It is foimd from New 
Jersey west to Nebraska and south to Florida 
and Texas. 

The only common species of Hapithus is H. 
agitator, which is found from Long Island west to 
Nebraska and south to Florida _ and Texas. 

Our only species of Tafalisca is T. lUrida, 
which is found in southern Florida. 

Subfamily CECANTHIN^ 

The Tree-Crickets Fig. 262.— Orocharis 

saltaior. (From 
These are delicate crickets, many of which are Lugger.) 
of a light green color, with the body and legs 
sometimes dusky. Figure 263 represents a male; in the females the 
front wings are miore closely wrapped about the body, giving the insect 
a narrower appearance. They live in more or less elevated positions, 
varying, according to the species, from among herbaceous plants to 
the higher parts of fruit and forest trees, hence the name tree-crickets 
commonly applied to them. Their frequent occurrence among flowers 
suggested the name of the principal genus, CEcdfithus, implying / 
dwell in flowers. Two genera of tree-crickets are represented in our 
fauna, Neoxahea and CEcanthus; these can be distinguished by differ- 
ences in the armature of the hind tibi«. 

Neoxahea. — In this genus the hind tibiae bear 
neither teeth nor spines except the apical spurs, 
and the first segment of the antennae is armed in 
front with a stout, blunt tooth (Fig. 264, h). 
Neoxahea bipunctdta is the only species known. 
In this species the hind wings are almost twice as 
long as the fore wings; the fore wings of the fe- 
male are each marked with two rather large 
blackish spots; the wings of the male are un- 
marked. The general color is pale pinkish brown. 
The length of the body is about 16 mm. 

CEcanthus .—In this genus the hind tibiae bear 
both spines and teeth. Several species occur in 
F" 26 —CEcanthus the United States and Canada; these differ in the 
^%veus male"" "'^ color of the body, in the markings on the first two 
segments of the antennas, in their song, and in the 




246 



AN INTRODUCTION TO ENTOMOLOGY 



elevation above the surface of the ground in which they are usually 
found. Most of our species are found east of the Great Plains; 
one, CEcanthus calif ornicus, occurs in California; and one, CEcanthus 



& 



« t 







Fig. 264. — Basal segments of antennae of QLcanthus and Neoxabea. (The lettering 
is explained in the text. (After Lugger and Fulton.) 

argentinus, in Texas. The species of eastern North America can 
be distinguished by the following table, which is copied from a de- 
tailed account of these insects by B. B. Fulton ('15). 

A. Basal segment of antennas with a swelling on the front and inner side. First 
and second segments each with a single lalack mark. 

B. Basal antennal segment with a round black spot. (Fig. 264, a). . ffi. nlveus 
BB. Basal antennal segment with a J-shaped black mark. (Fig. 264, b) 

CE. angustipcnnis 

BBB. Basal antennal segment with a straight club-shaped black mark. 

(Fig. 264, e) ffi. exclamationis 

AA. Basal antennal segment without a swelling on the front and inner side. 

First and second antennal segments each with two black marks or entirely 

black. Tegmina of males 5 mm. or less in width. 

B. Head and thorax pale yellowish green or black or marked with both colors. 

C. First antennal segment with a narrow black line along inner edge and a 

black spot near the distal end. Body entirely pale yellowish green. (Fig. 

264, d) ffi, quadripunctatus 

CC. First antennal segment with black markings similar to above, but 

broader and usually confluent, sometimes covering the whole segment. 

Head and thorax often with three longitudinal black stripes; ventral 

side of abdomen always solid black in life. (Fig. 264, c) . . CE. nigricornis 

BB. Head, thorax, and antennas reddish brown. Wings in life with conspicuous 

green veins. Marks on basal antennal segment broad but seldom con. 

fluent. (Fig. 264, f) (E. pini 

AAA. Basal antennal segment without a swelling on the front and inner side. 
Basal portion of antenna red unmarked with black. (Fig. 264, g). Teg- 
mina of male about 8 mm. wide (E. latipennis 

The species of CEcanthus that most often attracts attention is 
the snowy tree-cricket, CEcanthus niveus (Fig. 263). The pres- 
ence of this insect, though usually unseen, is made very evident in late 



ORTHOPTERA 



247 



summer and in the autumn by the song of th e males . This song is begun 
early in the evening and is continued through- 
out the night ; it consists of a monotonous series 
of high-pitched trills rhythmically repeated in- 
definitely. It is a remarkable fact that all of 
these crickets that are chirping in any locality 
chirp in unison. Individual singers will stop 
to rest, but when they start again they keep 
time with those that have continued the chorus , 
Except where the true katydid is heard, this is 
the most conspicuous insect song heard in the 
night in the regions where this species occurs. 
This cricket inhabits chiefly high shrubs and 
trees; it deposits its eggs singly in the bark or 
cambiiun of trees and bushes. 

While the presence of the snowy tree-cricket 
is made evident by its song, there is another 
species that has attracted much attention by 
its manner of oviposition; this is Qicanthus 
nigricornis. The female lays her eggs in a 
longitudinal series in the twigs or canes of 
various plants (Fig. 265). She selects the rasp- 
berry more often than any other plant; and 
as that portion of the cane beyond the incisions 
made for the eggs usually dies, it often happens 
that these crickets materially injure the plants. Fig. 265.— Stem of black 
In such cases the dead canes should be cut out raspberry with the eggs 

1 . J 1 • ^1 • 1 r xi of (Ecanthus mgrtcor- 

and burned early m the sprmg before the eggs „^-^ . ^^ ^^ ggg enlarged. 

hatch. (From Riley.) 




Subfamily GRYLLIN^ 



TJw Field-Crickets 



The field-crickets abound everywhere, in pastures, meadows, and 
gardens; and certain species enter our dwellings. They lurk imder 
stones or other objects on the ground or burrow into the earth. 
They are chiefly solitary, nocturnal insects; yet many can be seen 
in the fields in the daytime. They usually feed upon plants but are 
sometimes predacious. With most species the eggs are laid in the 
autumn, usually in the grotmd, and are hatched in the following 
summer. The greater number of the old crickets die on the approach 
of winter; but a few survive the cold season. In many of the species 
there are both short-winged and long-winged forms. 

This subfamily is represented in our fauna by several genera; 
but nearly all of our common species are included in the two genera 
Gryllus and Nemohius. 



248 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. 266 
sus. 



-Gryllus assimilis luctuo- 



The larger field-crickets, Gryllus. — The members of this genus are 
dark-colored, thick-bodied insects of medium or large size. In these 

the hind tibiae are armed with strong 
fixed spines and the first segment of 
the hind tarsi is armed with two 
rows of teeth above. There are 
two auditory tympana in each fore 
tibia. The length of the body is 
rarely less than 14 mm. 

Many supposedly distinct 
species of Gryllus have been de- 
scribed as occurring in our faima; 
but now all of our native forms are believed to be merely varieties of 
one species, Gryllus assimilis, and the different varieties are distin- 
guished by subspecific names. Six of these varieties that occur in 
the East are described by Blatchley ('20). Two of these will serve 
to illustrate our native forms. 

Gryllus assimilis luciudsus. — This is one of our more common 
forms of the genus. It is distinguished by the great length of the 
ovipositor of the female, which is nearly or 
fully half as long again as the hind femora 
(Fig. 266) ; and by the fact that the head of 
the male is distinctly wider than the front 
of the pronotum. 

Gryllus assimilis pennsylvanicus. — In 
this variety the ovipositor is less than half 
as long again as the hind femora, and the 
head of the male is but little if any wider 
than the front of the pronotum (Fig. 267). 
In fresh specimens the color is not shining 
black, but with a very fine grayish pubes- 
cence. 

In addition to our native forms of Gryllus, 
there is an Old World species that has been 
introduced into this country; this is the 
house-cricket, Gryllus domesticus. Refer- 
ences to the "cricket of the hearth" are 
common in English literature and refer to 
this species, which is now widely distributed 
in this country, though it is rarely abundant. 
It is pale yellowish browTi or straw-colored, 
and slender in form (Fig. 268). The length 
of the body is 15-17 mm. 

Our native field-crickets sometimes enter 
our dwellings in the autumn; but the house-cricket can be easily 
distinguished from these. 

The smaller field-crickets, Nemobius. — To this genus belong the 
little field-crickets, which are the most abundant of all of our crickets. 
In these the hind tibiae are furnished with long, mobile, hairy spines. 




Fig. 267. — Gryllus assim- 
ilis pennsylvani- 
cus. (From Lugger.) 



ORTHOPTERA 



249 



and the first segment of the hind tarsi is unarmed above or with only 
one row of teeth. There is only one tympantim in each fore tibia. 
The length of the body is less than 1 2 mm. 

There are many species and varieties of this genus in our fauna. 
The following enlarged figures of two of our species will serve to 
illustrate the form of these insects. (Fig. 269 and 270.) 






Fig. 268.— Gryllus do- 
mesticus. (From Lug- 
ger.) 



Fig. 269. — • Nemo- 
bius fasciatus. 
(From Lugger.) 



Fig. 270. — Nemo- 
bins pahistris. 
(Fom Blatch- 
ley.) 



Subfamily MYRMECOPHILIN^ 

The Ant-loving Crickets 

The members of this subfamily are very small crickets, which live 
as guests in the nests of ants. 
The form of these crickets is very 
remarkable. The body is ovate, 
greatly convex above, and wing- 
less (Fig. 271); the hind femora 
are ovate and greatly enlarged, 
the cerci are long; and the ovi- 
positor is short and stout. 

Wheeler ('00) states that 
these crickets feed on an oily 
secretion covering the surface of 
the body of the ants; they also 
obtain this substance from the 
greasy walls of the ant-burrows. 
Apparently the ants derive no benefit from the presence of these 




Fig. 271. — Myrmecophila pergandei. 
(From Lugger.) 



250 AN INTRODUCTION TO ENTOMOLOGY 

guests, and destroy them when they can; but the crickets are very 
agile. These are the smallest of the true Orthoptera. 

This subfamily includes a single genus, Myrmecophila, of which 
five species have been described from the United States. Only one 
species has been found in the East; this is Myrmecophila pergdndei. 
In this species the length of the body is 3-5 mm. 



Subfamily MOGOPLISTIN.E 

The Wingless Bush-Crickets 

These crickets are found chiefly on bushes or among rubbish under 
bushes; some are found beneath debris in sandy places. They are 

small; those found in the 

United States measure from 

5 mm. to 13 mm. in length of 

body. They are either wing- 
less or furnished in the male 

sex with short tegmina, in 

which the stridulating organs 

are well developed. The body 

is covered with translucent, 

easily abraded scales. 

Most of the species are 

tropical or subtropical in dis- 
tribution; our species are 

found chiefly in the South and 

Fig. 2j2.^Cryptopti- Southwest; but the range of 

him trigonipalpiim. one of them extends north to Fig- 273. — Holosphy- 

(From Rehn and Long Island. Only four spe- rum boreale {From 

Hebard. ^:^^u^,.^u ^^r,L:u^A ^'^ Rehn and He- 





cies have been described from 



bard.) 



the East and one of these is 
restricted to Florida. A few others are known from the western part 
of our countr>\ A monograph of the North American species was 
published by Rehn and Hebard ('12). 

Figure 272 represents the male of Cryptoptilum trigonipdlpum, sl 
wingless species found from Virginia southward; and Figure 273, the 
male of Holosphyrum boreale, found in the Southwest. 



Subfamily GRYLLOTALPIN^ 

The Mole-Crickets 

The mole-crickets differ greatly in appearance from the more 
typical crickets, the form of the body and of the fore legs being 
adapted to burrowing in the ground. The front tibiae, especially, 
are fitted for digging; they are greatly broadened and shaped some- 



ORTHOPTERA 



251 




what like a hand or a foot of a mole ; they are terminated by strong 

blade-like teeth, termed the dactyls (Fig. 274). 

Two of the tarsal segments are blade-like and so situated that 

they can be moved across the dactyls like the 

cutting blades of a mowing machine (Fig. 275). 

Sharpe ('95) states that this organ enables the 

mole-cricket to cut the small roots it meets in 

digging its burrows ; but this is doubted by Morse 

('20), who believes that the roots are cut by the 

powerful mandibles. 

The antennse of mole-crickets are much shorter 

than the body; the hind femora are but little 

enlarged, not well fitted for jumping; and the 

ovipositor is not visible externally. The name of 

the type genus, Gryllotalpa, is from Grylhis, a 

cricket, and talpa, a mole. 

Two genera of mole-crickets are found in the 

United States: Gryllotalpa, in which the front 

tibias are furnished with four dactyls; and Scap- 

tenscus, in which each fore tibia bears only two 

dactyls. Each of these genera is represented in 

our fauna by several species. 

Our best-known and most widely distributed 

species is Gryllotalpa hexaddctyla (Fig. 274). This 

species has been generally known in this country as Gryllotalpa 

horedlis; but this name is now be- 
lieved to be a synonym. The 
range of this species extends from 
British America to the southern 
part of South America. The 
length of the body is 20-30 mm. 
The mole-crickets are not 
common insects in this country; 
but occasionally they are found 
in great numbers in a limited lo- 
cality. They make burrows in 
moist places from six to eight 
inches below the surface of the 
ground, and feed upon the tender 
roots of various plants, and also 
on other insects. The eggs are 
deposited in a neatly constructed 
subterranean chamber, about the 
size of a hen's eee. 



Fig. 274. — Gryllotal- 
pa hexadactyla. 




Fig. 275. — Front leg of a mole-cricket; 
A, inner aspect; B, outer aspect; e, 
ear-slit. (Prom Sharp.) 



Subfamily TRIDACTYLIN^ 

The Pigmy Mole-Crickets 

The members of this subfamily resemble the mole-crickets in the 
form of the body and in their burrowing habits; but they are much 




252 A N INTROD UCTION TO ENTOMOLOG Y 

smaller, the larger species measuring only lo mm. in length; and the 
hind femora are greatly enlarged, being strongly saltatorial (Fig. 276). 
The antennae are short and composed of only eleven 
segments. The fore wings are usually short and 
never extend to the end of the abdomen; they are 
horny, are almost veinless, and are not furnished 
with stridulating organs in the male. The hind wings 
are much longer, usually extending beyond the end 
of the abdomen. The fore tibiae lack auditory 
tympana. The first four tarsi, in our genera, are 
two- jointed; the hind tarsi are one- jointed or want- 
ing. The hind tibiae are furnished with movable 
plates, "natatory lamellae," near the distal end; these 
are ordinarily closely appressed to the tibia but can 

be spread out like a fan. It is probable that these p- 2-5 tH- 

plates are used to aid the insect in leaping from the dactylns apica- 
surf ace of water upon which they have jumped ; lis. (From Lug- 
they may also serve a similar purpose on land, mak- sev.) 
ing a firm planting of the end of the leg upon the 
ground. The ovipositor is vestigial in our species; but Walker ('19) 
states that in the exotic genus Ripipteryx there is a well-developed 
ovipositor, which is remarkably similar to that of the short-horned 
grasshoppers. These insects apparently have two pairs of cerci; this 
is due to the fact that in addition to the true cerci each of the two 
podical plates is greatly elongated and bears a terminal segment, 
which appears like a stylus or cercus. 

These insects burrow rapidly in sand and possess great powers of 
leaping. They live on and in the damp sand on the shores of ponds 
and streams. Their burrows extend only a short distance below the 
surface of the ground. 

Only two genera, each represented by a single species, have been 
found in America north of Mexico. 

Triddctylus. — In this genus the hind tibiae are furnished with four 
pairs of long, slender plates, the "natatory lamellae;" and the hind 
tarsi are one-jointed. Our species is Triddctylus apicdlis (Fig. 276). 
Thejength of the body is 6-9.5 m^i- 

Ellipes. — In this genus the hind tibiae are furnished with a single 
pair of "natatory lamellae"; and the hind tarsi are wanting. Our 
vSpecies is Ellipes minida. The length of the body is 4-5 mm. 

Walker ('19) as a result of his studies of the genitalia of Ripi- 
pteryx believes that the pigmy mole-crickets are more closely allied 
to the Locus tidae than they are to the Gryllidae, and ranks them as 
constituting a distinct family, the Tridactylidae. 

Family LOCUSTID^* 
The Locusts or Short-horned Grasshoppers 
The family Locustidae includes the locusts or short-horned grass- 

*This family is termed the Acrididse by some writers, this name being based on 
the generic name Acrida of Linnaeus; other writers use the family name Aery- 



ORTHOPTERA 253 

hoppers. These are common and well-loiown insects. They differ 
from most of the members of the two preceding famiHes in having 
the antennee much shorter than the body, and consisting of not more 
than twenty-five segments. The ovipositor of the female is snort 
and composed of separate plates; and the basal segment of the 
abdomen is furnished on each side with a tympanum, the external 
parts of the organs of hearing (Fig. 277, t). 

It is to these insects that the term locust is properly applied; 
for the locusts of which we read in the Bible, and in other books 
published in the older countries, are members of this family. 
Unfortunately, in the United States the term locust has been applied 
to the Periodical Cicada, a member of the order Homoptera, described 
later. And, what is more unfortunate, the scientific name Locus- 
tidse has been applied by many writers to the long-homed 
grasshoppers. 

Locusts lay their eggs in oval masses and cover them with a 
tough substance. Some species lay their eggs in the ground. The 
female makes a hole in the ground with her ovipositor, which is a 
good digging tool. Some species even make holes in fence-rails, logs, 
and stumps; then, after the eggs are laid the hole is covered up with 
a plug of gummy material. There is but one generation a year, and 
in most cases the winter is passed in the egg-state. This family is 
of great economic importance, as the members of it usually appear in 
great numbers in nearly every region where plants grow, and often 
do much damage. 

With many species of the Locustidae the males are furnished with 
stridulating organs. These have been described in Chapter II, 
page 82. 

There are very many species of locusts in the United States and 
Canada; these represent four of the subfamilies of the family Locus- 
tidae, which can be separated by the following table. 

A. Claws of the tarsi with a small pad (arolium) between them; pronotum ex- 
tending at most over the extreme base of the abdomen. 
B . Prosternum armed anteriorly with a distinct conical or cylindrical tubercle. 

p. 254 LoCUSTINiE. 

BB. Prosternum without a distinct tubercle; arolium usually small or rather 
small. 
C. Head rounded at the union of the vertex and front ; front perpendicular 

or nearly so. p. 257 CEdipodin^. 

CC. Vertex and front of head meeting at an acute angle; vertex extending 

horizontally; front strongly receding, p. 259 Truxalin^. 

AA. Claws of tarsi without an arolium between them; pronotum extending over 
the abdomen, p. 259 Acrydiin^. 



diidse, based on the generic name Acrydium of Fabricius; and still others use the 
family name Acridiidae, based on Acridium, an emended spelling of Acrydium. 
The oldest name given to this family is Acrydiana, applied to it by Latreille in 
1802; but the group of insects that Latreille used as the type of the family is the 
Locusta of Linnaeus (1758); for this reason the name given to the family by 
Latreille has been changed to Locustidae. See also the footnote on page 234. 



254 



AN INTRODUCTION TO ENTOMOLOGY 



Subfamily LOCUSTIN^ 

The Spur-throated Locusts 

The members of this subfamily are distinguished from other 
North American locusts by the presence of a tubercle on the pro- 
sternum. Here belong 
many of our more com- 
mon species; and among 
them are found the most 
injurious insects of the 
order Orthoptera. Among 
our best -known species 
are the following. 

The Rocky Mountain 
locust or western grasshopper, Melanoplus spretus. — The most terrible 
of insect scourges that this country has known have been the invasions 




Fig. 277. — Side view of a female locust with the 
wings removed. 




Fig. 278. — Egg-laying of the Rocky Mountain Locust : a, a, a, female in different 
positions, ovipositing; b, egg-pod extracted from the ground with the end 
broken open; c, a few eggs lying loose on the ground; d, e, show the earth 
partially removed, to illustrate an egg-mass already in place, and one being 
placed; / shows where such a mass has been covered up. (From Riley.) 

of this species. Large areas of coimtry have been devastated, and the 
inhabitants reduced to a state of starvation. The cause of all this 
stiff ering is not a large insect. It is represented in natural size by 
Figure 278. It measures to the tip of its 
wing-covers 20-35 mm., and resembles 
very closely our common red-legged lo- 
cust, the most abundant of all our species. 
It can easily be distinguished from this 
species by the greater length of the wings, 
which extend about one-third of their 
length beyond the tip of the abdomen, 
and by the fact that the apex of the last 
abdominal segment in the males is distinctly notched. 




Fig. 279. — Melanoplus femur- 
rubrum. 



ORTHOPTERA 



255 




Fig. 280.- 
Riley.) 



-Melanoplus bivittatus. (From 



The permanent home or breeding grounds of this species is in the 
high, drylands on the eastern slope of the Rocky Mountains, extend- 
ing from the southern limit of the true forests in British America 
south through Montana, Wyoming, the western part of the Dakotas, 
and the Parks of Colorado. There are also regions in which the species 
exists permanently west of 
the Rocky Mountains in 
Idaho and Utah. 

When the food of this 
insect becomes scarce in its 
mountain home, it migrates 
to lower and more fertile re- 
gions. Its long wings en- 
able it to travel great dis- 
tances; and thus the larger 
part of the region west of the Mississippi River is liable to be invaded 
by it. Fortunately, the species cannot long survive in the low, moist 
regions of the valleys. Although the hordes of locusts which reach 
these sections retain their vigor, and frequently consume every bit 
of green vegetation, the yoimg, which 
hatch from the eggs that they lay, perish 
before reaching maturity. In this way 
the invaded region is freed from the pest 
until it is stocked again by another in- 
cursion. There is, however, a large sec- 
tion of country lying immediately east of 
the great area indicated above as the 
permanent home of this species, w^hich it 
frequently invades and in which it can 
perpetuate itself for several years, but 
from which it in time disappears. This 
sub-permanent region, as it has been 
termed, extends east in British America 
so as to include nearly one-third of Mani- 
toba; and, in the United States, it em- 
braces nearly the whole of the Dakotas, 
the western half of Nebraska, and the 
northeast fourth of Colorado. 

The temporary region, or that only 
periodically visited and from which the 
species generally disappears within a year, 
extends east and south so as to include 
more than half of Minnesota and Iowa, 
the western tier of counties of Missouri, 
the whole of Kansas and Oklahoma, and the greater part of 
Texas. The country lying east of the section thus indicated has 
never been invaded by this locust, and there is no probability that 
It will ever be reached by it. 




Fig. 281. — Melanoplus bivitta- 
tus killed by a fungus. 
(From Lugger.) 



256 



AN INTRODUCTION TO ENTOMOLOGY 



Detailed directions for the control of this pest have been pub- 
lished in many State and Federal Government reports. Among these 

methods of control are 
the plowing of land in 
which its eggs have 
been deposited, the 
use of poisoned bran- 
mash as a bait, and 
catching of the insects 
Fig. 282. — Melanoplus differentialis. (From Riley.) j^y machines com- 
monly known as "hopper dozers." 

The red-legged locust, Melanoplus femur-rubrum. — This is the 





Fig. 283. — Schistocerca americana. (From Riley.) 

most common short-horned grasshopper throughout the United 

vStates, except where Melanoplus 

spretus occurs. It ravages our 

meadows and pastures more than all other 

species combined. It is ioxmd in most 

parts of North America. The female is 

represented, natural size, by Figure 279. 

Melanoplus hivittdtus. — This species 
is also found from the Atlantic to the 
Pacific. It is marked with a yellowish 
stripe, extending along each side from 
the upper angle of the eye to the tip of 
the front wing (Fig. 280). The length of 
the body varies from 23 mm. to 40 mm. 

This locust is often killed by a para- 
sitic fungus. Dead fungus-infected in- 
dividuals are frequently found clinging to 
weeds, up which they have climbed to 
die (Fig. 281). 

Melanoplus differentialis. — This spe- 
cies is slightly larger than the preceding; 
and it lacks the prominent yellow stripe 
(Fig. 282). 

Schistocerca americana. — This magnifi- 
cent species occurs in the Southern States pjg. 2H^-Brachystoi^ mafKa. 
and has been foimd as far north as Con- (From Riley.) 




ORTHOPTERA 



257 



necfcicut and Iowa. It can be recognized by Figure 283, which rep- 
i-esents it natural size. This locust sometimes assumes the migratory 
' - injurious to agriculture. 



habit, and is sometimes 



The lubber grasshopper, Erachystola magna. — This 
clumsy species in which the wings are vestigial (Fig. 
confined to the central portion of North America. 

Leptysma marginicollis. — 
In most of the spur-throated 
locusts the face is nearly ver- 
tical; but in a few species it 
is very oblique. This species 
is a good illustration of this 
type (Fig. 285); it is foimd in 
the Southern States east of the 
Mississippi River. 



is a large, 
284); it is 




Fig. 28^.— Lcplysma marrinicollis. 



Subfamily CEDIPODIN^ 



The Bard-winged Locusts 



In this subfamily the prosternum is without a distinct tubercle; 
the head is rounded at the union of the vertex and the front; and the 
f'-ont is perpendicular or nearly so. In most of our species the hind 
wings are in part black, and a portion of them yellow or red; this 
gives them a banded appearance. There are many representatives 
of this subfamily in our fauna: the following are some of the more 
common ones. 

The clouded locust, Encoptolophus sordidus. — This species (Fig. 
286) is very common in the eastern United States during the autumn. 

It abounds in meadows and pas- 
tures, and attracts attention by 
the crackling somid made by the 
males during flight. It is of a 
dirty brown color, mottled with 
spots of a darker shade. The 
length of the body of the male is 1 9- 
-Encoptolophus sordidus. 22 mm.; of the female, 24-32 mm. 

The northern green-striped locust, Chortophaga viridifascidta. — 
This is a. very common species in the United States and Canada east 
of the Rocky Moim tains. There are two well-marked varieties, 
.'n one. the typical form, the head, thorax, and femora are 
green, and there is a broad green stripe on each fore wing, extend- 




Fig. 286. 



258 



AN INTRODUCTION TO ENTOMOLOGY 



ing 



to beyond 




t^^e middle; this often includes 
two dusky spots on the 
edge. In the other vari- 
ety, the ground color is 
dusky brown. Intergrades 
occur, in which the head 
and thorax are of a reddish 
velvety brown. The length 
of the body is 17-32 mm. 

The Carolina locust, 
D-issostetra Carolina. — Not- 
withstanding its specific 
name, this species is com- 
mon throughout the United 
vStates and Canada. It is 
a large species; the length 
of the body of the males is 
24-33 mm., of the females 
33-40 mm. It abounds in 
highways and in barren 

_,.__,.. ,- /T7 T ^ places. It takes flight 

Fig. 287.-Z)z..../.zraca../^na. (From Lugger.) ^^^^.^^^ ^^^ ^^^ ^^^^^ 

stridulate while in the air. The color of this insect varies greatly, 
simulating that of the soil upon which 
it is foimd. It is usually of a pale yel- 
lowish or reddish brown, with small 
dusky spots. The hind wings are black, 
with a broad yellow margin which is 
covered with dusky spots at the tip 
(Fig. 287). 

Boll's locust, Sphardgernon bolli. — 
This species is widely distributed in the 
United States and southern Ontario 
east of the Rocky Motrntains. The 
length of the body of the male is 20-28 
mm., of the female 27-36 mm. The 
hind wings are pale greenish yellow at 
the base and are crossed by a dark 
band; the apical third is transparent 
smoky in color (Fig. 288). 

The coral-winged locust, Hipptscus 
apiculdtus. — This is one of the larger 
of our band-winged locusts (Fig. 289). 
The length of the body of the male is 
25-30 mm., of the female 36-44 mm. The general color is ash-brown. 
The basal portion of the hind wings is bright coral-red, rarely yellow; 
this part is bordered without by a dark band. This species is widely 
distributed east of the Rocky Mountains. 




Fig. 288. — -Spharagemoji bolli. 
(From Lugger.) 



ORTHOPTERA 



259 




Fig. 289. — Hippiscus apiciilatus. (From Lugger.) 

Subfamily TRUXALIN^ 

The Slant-faced Locusts 




Fig. 2go.^Chloealtis conspersa, 
male. (From Lugger.) 



In this subfamily, as in the preceding one, the prostemum is 
unarmed but the head is of a different form. In the TruxaHnae, 

the v^ertex and the front meet on an 
acute angle. In some species this 
angle is a sharp one, the shape of 
the head being similar to that of 
Leptysnia (Fig. 285). In other 
species, however, the front is less 
receding ; this is the case in the fol- 
lowing species. 

The sprinkled locust, Chlo'ealtis 
conspersa. — This is a veryabimdant 
species in the northern United 
States and Canada east of 
the Great Plains. It is 
brown, with the sides of the 
pronotum and the first two 
or three abdominal seg- 
ments shining black in the 
male; and with the body 
and tegmina of the female 
sprinkled or mottled with 
darker brown. The teg- 
mina and hind wings are a 

little shorter than the abdomen in the male (Fig. 290), and much 
shorter in the female (Fig. 291). The males measure 15-20 mm. in 
length; the females, 20-28 mm. 




Fig. 2gi .—Chloealtis conspersa, female. (From 

Lugger.) 



Subfamily ACRYDIIN^ 

The Pigmy Locusts 

The Acry^diinae includes small locusts of very unusual form. 
They differ so much from other locustids that some students of the 



260 



AN INTRODUCTION TO ENTOMOLOGY 



Fig. 292.— A pig- 
my locust. 




Fig. 293. — Acrydium granula'.um. 
ley, after Kirby.) 



(From Blatch- 



Orthoptera believe they constitute a separate family. The most 
striking character of the subfamily is the 
shape of the pronotum. This is prolong- 
ed backwards over the abdomen to or beyond 
its extremity (Fig. 292). The head is deeply 
set in the pronotum; and the prosternum is ex- 
panded into a broad border, which partly 
envelops the mouth-parts like a muffler. The antennee are very 
slender and short. The tegmina are vestigial, being in the form of 
small, rough scales; while the wings are usually well-developed. 
These locusts differ, also, 
from all others in having 
no arolium between the 
claws of the tarsi. 

The pigmy locusts are 
commonly found in low, 
wet places, and on the 
borders of streams. 
Their colors are usually 
dark, and are often pro- 
tective, closely resem- 
bling the soil upon which 
the insects occur. They 
are very active and pos- 
sess great leaping powers. 

Some of the species vary greatly in coloring; this has resulted 
often in a single species being described under two or more names. 
This is an exceedingly difficult group in which 
to deteiTnine the species. 

Figure 293 represents Acrydium granuldtum 
with its wings spread, and the pronota of two 
color varieties. 

Figure 294 represents Acrydium arenosum 
obsciirum, greatly enlarged, with its wings 
closed. 

Family PHASMID^* 
The Walking-Sticks and tJie Leaf -Insects 

The Phasmidee is of especial interest on ac- 
count of the remarkable mimetic forms of the 
insects comprising it. In those species that 
are fotmd in the United States, except one in 
Florida, the body is linear (Fig. 295), wingless, 
and furnished with long legs and antennae. This peculiar form 
has suggested the name walking-sticks which is commonly applied 

*This family is separated from the Orthoptera by Handlirsch ('o6-'o8) and 
made to constitute a distinct order, the Phasmoidea. 




Fig. 294. — Acrydium 
arenosum obscurum. 
(From Hancock.) 



ORTHOPTERA 



261 



to these insects; they are also kno\\ai as stick-insects. In some 
exotic species the body has the appearance of being covered with 
moss or with Hchens. which increases the resemblance to a stick 
or a piece of bark. 

While our species are all wingless, except Aplopus mayeri, found 
in southern Florida, many exotic species are furnished with wings; 
and with some of these the wings resemble leaves. Among the 
more remarkable of the leaf-insects, as they are kno\\Ti, are those 
of the genus PhylUum (Fig. 296), the members of which occur in 
the tropical regions of the Old World. 

In the walking-sticks, the body is elongate and subcylindrical. 
the abdomen consists of ten segments, but the basal segment is 
small and usually coalesced with the meta thorax and sometimes it 
is entirely invisible; the legs are all fitted for walking, the tarsi 
are five-jointed except in the genus Timema, where they are three= 
jointed; the cerci are without joints. _ 

These insects are strictly herbivorous; 
they are slow in their motions, and often 
remain quiet for a long time in one place. 
They evidenth' depend on their mimetic 
form for protection. In addition to this 
some species have the power of ejecting a 
stinking fluid, which is said to be very 
acrid ; this fluid comes from glands placed 
in the thorax. 

The eggs are scattered on the ground 
beneath the plants upon which the insects 
feed, the female, unlike most Orthoptera, 
making no provision for their safety. In 
our common northern species the eggs are 
dropped late in the summer and do not 
hatch till the following spring, and they 
often remain till the second spring before 
they hatch. 

About 600 species of phasmids have 
been described; but they are largely 
restricted to the tropical and subtropical 
regions. Caudell ('03) in his monograph 
of the species of the United States enu- 
merates sixteen species that occur in our 
fauna; but these are found chiefly in the 
southern part of the country. 

Our common northern walking-stick 
is Diapheromera femordta (Fig. 295). The 
range of this species extends into Canada. 
It is a quite common insect, and on sev- 
eral occasions has appeared in such great 
numbers as to be seriously destructive to 
the foliage of forest trees; but these outbreaks have been temporary. 




Diapheromera fem 



262 



AN INTRODUCTION TO ENTOMOLOGY 




Among the more striking in ap- 
pearance of the walking-sticks found 
in the South are Me gaphdsma de^itricus , 
our largest species, measuring from 125 
to 150 mm. in length, and Anisomorpha 
buprestoides, a yellowish brown species, 
about half as long as the preceding, 
with conspicuous, broad, black stripes 
extending from the front of the head 
to the tip of the abdomen. 

The reproduction of lost legs occurs 
frequently in this family. 



Family MANTID^^ 



The Praying Mantes or Soothsayers 



The praying mantes are easily rec- 
Fig. 296.— Phyllium scythe. (From ognized by the imusual forrn of the 
Sharp, after Westwood.) prothoraxand of the first pair of legs 

(Fig. 297). The prothorax is elongate, sometimes nearly as long as 
the remainder of the body; and the front legs are large and fitted 
for seizing prey. The coxee of the front legs are very long, pre- 
senting the appearance of femora; and the femora and tibi« of 
these legs are armed with spines; the tibia of each leg can be 
folded back against the femur so that the spines of the two will 
securely hold any insect seized by the praying mantis. 

The second and third pairs of legs are simple and similar; the 
tarsi are five-jointed; and the cerci are jointed. 

With some species the wings resemble leaves of plants in form 
and coloring. This resemblance is protective, causing the insects 
to resemble twigs of the plants upon which they are. 

All of the species are carnivorous, feeding on other insects. 
They do not pursue their prey but wait patiently with the front 
legs raised like uplifted hands in prayer, until it comes within reach, 
when they seize it. This position, which they assume while waiting, 
gives them most of their popular names, of which there are many. 

The eggs of the Mantidae are encased in chambered oothecas, 
which are usually fastened to the stems or twigs of plants (Fig. 298). 
In the case of the species that occur in the North, there is only 
one generation in a year and the winter is passed in the egg-state. 

Most of the members of this family are tropical insects ; a few 
species, probably less than twenty, live in the southern half of 



*This family is separated from the Orthoptera by Handlirsch ('o6-'o8) and 
made to constitute a distinct order, the Mantoidea. 



ORTHOPTERA 263 

the United States; and one of our native species, Stagmomdntis 




Fig. 297. — Stagmomantis Carolina 



Carolina (Fig. 297), is found as far north as Maryland 
and southern Indiana. 

Recently two exotic species have been introduced 
into the Northern States, probably by the irnporta- 
tion of oothecce on nursery stock, and have become 
established here. These are the Mantis religidsa of 
Europe, which was first observed in this country 
near Rochester, N. Y., in 1899, and Paratenodera 
sinensis of China and Japan, which was first ob- 
served here at Philadelphia about 1895. 



Family BLATTID^E* 

The Cockroaches 

The cockroaches are such well-known insects that 
there is but little need for a detailed account of their 
characteristics. As already indicated in the table of 
families, the body is oval and depressed; the head is 
nearly horizontal, and wholly or almost wholly 
withdrawn beneath the pronotum; the head is bent 
so that the mouth-parts project caudad between 
the bases of the first pair of legs; the antennas are 
long and bristle-like; and the pronotum is shield-like. 
This family includes only the cockroaches ; but these Fig. 298. — Egg- 
insects are known in some localities as "black ^^^^^ °f. ^^^^' 
, , ,, 1 J • • J.1 momantts car- 

beetles, and our most common species m the ^^^^^ (From 

northern cities bears the name of Croton-bug. Riley.) 




*This family is separated from the Orthoptera by Handlirsch ('o6-'o8) and 
made to constitute a distinct order, the Blattoidea. 



264 AN INTRODUCTION TO ENTOMOLOGY 

In the Northern States our native species are usually foimd in 
the fields or forests under sticks, stones, or other rubbish. But 
certain imported species become pests in dwell- 
ings. In the warmer parts of the coimtry, how- 
ever, native and foreign species alike swarm in 
Fig. 299.— Ootheca of a buildings of all kinds, and are very common out 
of doors. 



cockroach. 



Cockroaches are very general feeders; they destroy nearly all 
forms of provisions, and injure many other kinds of merchandise. 
They often deface the covers of cloth-bound books, eating blotches 
upon them for the sake of the sizing used in their manufacture ; and 
I have had them eat even the g\m\ from postage stamps. They thrive 
best in warm, damp situations; in dwellings they prefer the kitchens 
and laundries, and the neighborhood of steam and water pipes. They 
are chiefly nocturnal insects. They conceal themselves during the 
day beneath furniture or the floors, or within the spaces in the walls 
of a house; and at night they emerge in search of food. The de- 
pressed form of their bodies enables them to enter small cracks in 
the floors or walls. 

Not only are these insects very destructive to our possessions, but 
owing to their fetid odor merely the sight of them awakens disgust ; 
but it is due them to state that they are said to devour greedily bed- 
bugs. This will better enable us to abide their presence in our 
staterooms on ocean voyages, or in our chambers when we are forced 
to stop at poor hotels. 

The eggs of cockroaches are enclosed in purse-like capsules (Fig. 
299). These capsules, or oothecae, vary in form in different genera, 
but are more or less bean-shaped. Within, the ootheca is divided 
into two parallel spaces, in each of which there is a row of separate 
chambers, each chamber enclosing an egg. The female often carries 
an ootheca protruding from the end of the abdomen for several days. 
It has been found that a single female may produce several oothecae. 

The nymphs resemble the adults except in size, and, 
in the case of winged species, in the degree of develop- 
ment of the wings. In adults also of some species the 
wings are reduced, atrophied, or absent; this condi- 
tion exists more frequently in females than in males 
(Fig. 300). 

As in most other insects, the homologies of the 
wing-veins can be most easily determined by a study 
of the tracheation of the wings of nymphs; Figure 301 
will serve to illustrate this. 

Experiments conducted by the Bureau of Ento- 
mology at Washington have shown that one of the Fig-.3oo- — A 
most effective means of ridding premises of cockroaches wingless 
is dusting the places they frequent with commercial 
sodium fluorid. Several other substances are used for this purpose; 




ORTHOPTERA 



265 



among these are borax, p}'rethnun, sulphur, and phosphorus paste. 

Cockroaches are chiefly inhabitants of warm countries ; although 

nearly one thousand species have been described, few are found in the 




Fig. 301. — Fore wirg of a nymph of a cockroach. 

temperate regions. Only forty-three species have been found in 
North America north of the Mexican boimdary, and ten of these 
are probably introduced species (Hebard '17). ^ The cockroaches that 
are most often found in buildings are two introduced species, the 
Croton-bug and the Oriental cockroach, and two native species, the 
American cockroach and the common wood-cockroach. The adults 







Fig. 302. — The Croton-bug: a, first instar; h, second instar; c, third instar; d, 
fourth instar; e, adult; /, adult female with egg-case; g, egg-case, enlarged; 
h, adult with the wings spread. All natural size except g. (From Howard 
and Marlatt.) 

of these four species can be separated by the following table. For 
tables separating all North American species see Hebard ('17). 

A. With well-developed tegmina. 

B. Tegmina extending to or beyond the tip of the abdomen. 

C. Body about 12 mm. in length The Crototi-bug 

CC. Body 16 mm. or more in length. 



266 



AN INTRODUCTION TO ENTOMOLOGY 



D. Margin of the pronotum light in color while the disk is dark. . . 

The common wood-cockroach, male 

DD. Pronotum reddish-brown with two blotches of a lighter color. 

The American cockroach 

BB. Wings not extending to the tip of the abdomen. 

C. With a, light band on each lateral border of the pronotum 

The common wood-cockroach, female 

CC. With no bands on the pronotum The Oriental cockroach, male 

AA. Tegmina represented by small ovate pads The Oriental cockroach, 

female 

The Croton-bug, Blattella genndnica (Fig. 302), is the best-known 
of all of the cockroaches in our northern cities. It is easily recognized 
_ by its small size, about 

^- ,-— ^^ >V ^ ' 12 mm. in length, and 

^ '^^ by its pale color with 

two dark, parallel 
bands on the prono- 
tum. Its popular 
name originated in 
New York City, and 
was suggested by the 
fact that this pest is 
•^ \/ very abundant, in 

** '^ ^ houses, about water 

pipes connected with 
the Croton Aqueduct. 
This is a species intro- 
duced from Europe; 
it has spread to nearly 
^ ^ ^ r ^ y ^11 parts of the world, 

living upon ships, and 

Fig. 303.— The oriental cockroach: a, female; b, spreading from them. 

male, ^. side view of female; rf, half-grown sped- ^^j^e oriental cock- 

men. All natural size. (From Howard and Mar- , t,t-,, ■ j-i- 

latt.) roach, BLatta onentaUs 

(Fig. 303), is also a 
cosmopolitan species ; its original habitat is supposed to have been 
in Asia; but it has been distributed by commerce throughout the 
world except in the colder regions. In this country it is most abun- 
dant in the central latitudes of the United States; it has been foimd 
in only a few places in Canada. It measures from 18 to 25 mm. in 
length. It is blackish brown in color. In the male the wings cover 
about two-thirds of the abdomen ; while in the female they are small, 
ovate-lanceolate, lateral j^ads. 

The American cockroach, Periplaneta americdna (Fig. 304), is a 
native of tropical or subtropical America that has become distributed 
both in tropical and mild climates over the entire world. This is a 
large species measuring from 25 to 33 mm. in length. 

The common wood-cockroach, Parcobldtta pennsylvdnica, is a 
common species throughout the eastern half of the United States, 




ORTHOPTERA 267 

and its ranre extends into southern Canada. It is a na- 




The American cockroach. (From Howard and Marlatt.) 



tive of our woods but is frequently attracted to lights in our houses 
The two sexes differ 
so greatly in appear- 
ance that they were 
long believed to be 
distinct species. In 
both sexes the lateral 
margins of the prono- 
tum are light in color 
while the disk is dark. 
In the male the body 
measures from 15 to 
25 mm. in length and 
the wings extend be- 
yond the tip of the ab- 
domen (Fig. 305). The 

female is smaller and the wings are much shorter than in the mal 

(Fig. 306) 





Fig. 305. — The common 
wood-cockroach, male. 
(From Lugger.) 



Fig. 306. — The com- 
m o n wood-cock- 
roach , female. 
(From Blatchley.) 



ORTHOPTEROID INSECTS OF UNCERTAIN KINSHIP 

Under this head is placed a family of insects the zoological po- 
sition of which has not been definitely determined. 



268 ^A^ INTRODUCTION TO ENTOMOLOGY 

Family GRYLLOBLATTID^ 

This family was recently established by Dr. E. M. Walker ('14) 
for the reception of the species described below, which, while showing 
striking affinities to the Orthoptera, differs remarkably from all 
other known members of this order. Some writers who favor the 
breaking up of the order Orthoptera into several orders, regard this 
species as the type of a distinct order of insects, the Notoptera. 

Gryllobldtta campodeiformis. — In this the only species of the family 
known, the body is elongate, slender, depressed, and thysanuriform 




Fig. 307. — GrylloUatta campodeiformis. (After Walker.) 
(Fig. 307). The legs are fitted for rimning, the tarsi are five-jointed 
and lack pulvilli. The cerci are long, about as long as the hind tibiae, 
slender, and eight-jointed. The ovipositor is exserted and resembles 
that of the Tettigoniidas. The eyes are small and the ocelli are absent. 
The adult male measures 16.5 mm. in length; the female, 30 mm. 
As yet, this species has been fotmd only in the vicinity of Banff, 
Alberta, and in Plumas Coimty, California. It is found under stones, 
at high altitudes, and nms like a centipede. 



ORTHOPTERA 



269 



Family HEMIMERID^ 

Further studies of this family during the 
years since the pubHcation of former editions 
of the Introduction seem clearly to have estab- 
lished the affinity of the Hemimeridae with the 
order Dermaptera. Recent explorations and 
collections from rats of Africa have brought 
to light several new species in the family and 
much additional knowledge concerning their 
habits. We have, therefore, placed the family 
with a brief discussion of it under the Dermap- 
tera, on page 463. In 1925 Professor Comstock 
said concerning this family, "although these 
are exotic insects, they are mentioned here on 
account of their exceptional manner of devel- 
opment and mode of life." The additional 
knowledge concerning them emphasizes this 
observation and justifies retaining a brief 
discussion of the family among its proper 
relatives. 




Fig. 308. — Hemimerus 
hans eni. (From 
Hansen.) 



CHAPTER IX 
ORDER ZORAPTERA* 

So little is known regarding the insects of this order, only a single 
genus having been found, that it would be premature at this time 
to define definitely the characters of the order. This is well shown 
by the fact that recent discoveries have greatly modified our views 
regarding the ordinal characters of these insects. 

This order was established by Silvestri in i g 13 . At that time only 
wingless individuals were known; and it was supposed by this author 
that the wingless condition was a distinctive ordinal character; he, 
therefore, proposed the name Zoraptera for the order. But recently 
Caudell ('20) has described winged individuals of each of the two 
species fotmd in this country. The name Zoraptera, however, must 
be retained even though it is inappropriate. 

Family ZOROTYPIDiE 

The single known genus, Zorotypus, is the type of this family and 
imtil other genera are found the characters of this genus must be 
taken as those of this family and of the order Zoraptera as well. 

At the time this is written, only six species of Zorotypus have been 
described. These have been found in widely separated parts of the 
world, one each in Africa, Ceylon, Java, and Costa Rica, and two in 
Florida. One of the species from Florida has been found also in Texas. 

The knowTi species are all minute, the largest measuring only 2.5 
mm. in length. In our two species both wingless and winged adults 
have been foimd ; and it is probable that these two forms exist in the 
other species. The winged adults that have been observed are all 
females; but it would not be wise to conclude that only this sex is 
winged. Of the wingless form both male and female have been found. 
As these are social insects, living in colonies of various sizes, it may 
be that the wingless and the winged adults represent distinct castes, 
analogous to the castes of termites. Another similarity to termites 
is that the winged individuals shed their wings as do the winged 
termites. 

The wingless adults (Figure 309, 4) resemble in general appear- 
ance small worker termites ; but they have longer legs and are more 
active. The legs are formed for running; the tarsi are two-jointed 
and each bears two claws. The mandibles are strong. The antennae 
are moniliform and nine-jointed. Compound eyes and ocelli are 
wanting. The cerci are short, fleshy, and unsegmented. 

The winged adult female (Fig. 309, i) has large compound eyes, 
three ocelli, nine-jointed antennae, and two pairs of wings. The vena- 

*Zoraptera: zoros {suphs), pure; apterous (dTrrepos), without wings. 

(270) 



ZORAPTERA 



271 



tion of the wings is represented in the figure. As the tracheation of 
the wings of n\Tnphs has not been studied, I will not venture to make 
any suggestions regarding the homologies of the wing-veins. 




Pig n^oQ.—Zorotypus hubbardi: i, winged adult female; 2, adult female that had 
shed her wings; 3, nvmph of winged form; 4, wingless adult female. 5 -An- 
tenna of adult wingless Zorotypus snyderi. (From Caudell,m Proc. lint. boc. 
Wash., Vol. 22.) 



272 AN INTRODUCTION TO ENTOMOLOGY 

Figure 309, 2, represents an adult female that had shed her wings; 
and Figure 309, 3, a nymph with well-developed wing pads. 

The two known American species are Zorotypus hubhardi and 
Zorotypus snyderi. Detailed descriptions of each of the forms of 
each of these species are given by Caudell ('20), and the external 
anatomy of Zorotypus hubhardi is described by Crampton ('20 a), 
who also discusses the relationships of the order Zoraptera to the 
other orders of insects. 

The colonies of Zorotypus are found under the bark of logs and 
stumps and frequently near the galleries of termites. For this 
reason they were formerly believed to live as inquilines in the nests of 
termites ; but recent observations do not support this view« 




CHAPTER X 
ORDER ISOPTERA* 

The Termites or White- Ants 

The members of this order are social insects, living in colonies like 
ants. Each species consists of several distinct castes, the number of 
which differs in different species. Each caste includes both male and 
female individuals. In most species there are four castes as follows: 
first, the first reproductive caste, in which the wings become fidly de- 
veloped and are used for a swarming flight and then shed; second, the 
second reproductive caste, in which the wing-buds remain short; the 
members of this caste are neoteinic, becoming sexually mature while 
retaining the nymphal form of the body; third, the worker caste; and 
fourth, the soldier caste. Except in a single Australian genus, the two 
pairs of wings are similar in form and in the more general features of 
their venation; they are long and narrow, and are laid flat on the back 
when not in use. The abdomen is broadly joined to the thorax; the 
mouth-parts are formed for chewing; the metamorphosis is gradual. 

The termites or white-ants are chiefly tropical insects; but some 
species live in the temperate zones. These insects can be easily 
recognized by the fact that they live in ant-like colonies, by the pale 
color of the greater nimiber of individuals of which a colony is com- 
posed, and by the form of the abdomen, which is broadly joined to 
the thorax instead of being pedunculate as in ants. 

The termites are commonly called white-ants on account of their 
color and of a resemblance in form and habits to the true ants. 
These resemblances, however, are only very general. In structure 
the termites and ants are widely separated. In habits there is little 
more in common than that both are social, and the fact that in each 
the function of reproduction is restricted to a few individuals, while 
the greater number differ in form from the sexually perfect males and 
females, and are especially adapted to the performance of the labors 
and defense of the colony. 

The cuticula of termites is delicate even in adults; the mature 
winged forms can withstand exposure to dry air for a limited period, 
as is necessary during their swarming flight; but other members of 
a colony quickly become shriveled and die if exposed. It is for this 
reason that they build tubes constructed of earth and excrement for 
passage-ways, and only rarely appear in the open, and then merely 
for a brief period. 

The mouth-parts, which are fitted for chewing, are quite general- 
ized, resembling somewhat those of the Orthoptera; but in the case 
of the soldier caste the mandibles are very large and vary greatly in 
form in the different species. 

*Is6ptera: isos (f<roj), equal; pteron {irrephv), a wing. 
(273) 



274 



AN INTRODUCTION TO ENTOMOLOGY 



The antennas are moniliform; in the winged adults the number 
of segments varies in different species from twelve to twenty-five or 
more. In newly hatched nymphs the number of antennal segments 
is less than in the later instars. 

The members of the winged sexual caste have pigmented compound 
eyes and a pair of ocelli. It is commonly stated that both the workers 
and soldiers of termites are blind ; but in some species the soldiers 
have compound eyes ; these, however, are not pigmented. There is 
an African species, the marching termite, in which both workers and 
soldiers possess eyes (Fuller '12). 

The median ocellus is wanting in termites; but in many forms 
there is in its place a more or less distinct opening of a gland, the 
frontal gland, whose secretion is used for defense; this opening of 
the frontal gland is termed the fontanel or fontanelle or fenestra. 




Fig. 310. — Wings of Termopsis angusticollis. 

The wings are long and narrow, and, when folded on the back of 
the insect, extend far beyond the end of the abdomen. In the Aus- 
tralian genus Mastotermes, the anal area of the hind wings is broadly 
expanded; in other termites the fore and hind wings are similar in 
form (Fig. 310). In each case, the veins of the anterior part of the 
wing are greatly thickened and those of the middle portion reduced 
to indistinct bands or to narrow lines. Regular cross- veins are lack- 
ing, the membrane of the wings being strengthened by an irregular 
network of slightly chitinized wrinkles. The wings are deciduous, 
being shed after the swarming flight. The shedding of the wings is 
facilitated by the presence in each wing, except in the hind wings of 
certain genera, of a curved transverse suture, the humeral suture. 



T SOFTER A 275 

The homologies of the wing-veins are discussed by the writer in his 
"The Wings of Insects," Chapter VIII. 

The abdomen consists of ten visible segments and bears a pair of 
two- to six- jointed cerci. The genitalia are vestigial and are 
concealed by a backward prolongation of the stemttm of the seventh 
abdominal segment. 

If a colony of termites be examined, many kinds of individuals will 
be found. This multiplicity of forms is due partly to the fact that 
these insects imdergo a gradual metamorphosis, and n^-mphs of various 
sizes and degrees of development will be found running about among 
the mature individuals. But even if only adults be considered, it 
will be found that each species consists of several distinct castes. 

With the termites the number of castes is greater than with the 
social bees, social wasps, and ants; and each caste includes both male 
and female individuals. The termites differ also from other social 
insects in that there are at least two and sometimes three castes 
whose function is reproduction. The following castes have been 
foimd among these insects. 

The first reprodtictive caste. — ^At a certain season of the year, late 
spring or early summer for our most common species in the eastern 
United States, there can be found in the nests individuals with fully 
developed wings. These are sexually perfect males and females and 
constitute what is Icnown as the first reproductive caste. In these the 
cuticula is black or dark chestnut in color, the eyes are functional, 
and the wings project more than half their length beyond the end 
of the body. A little later, these winged individuals leave the nest 
in a body; sometimes clouds of them appear. After flying a greater 
or less distance they alight on the ground, and then shed their wings. 

At this time the males seek the females and they become associated 
in pairs ; but the fertilization of the females does not take place till 
later. It seems probable that in some cases swarms issue from 
different nests at the same time, as we know to be the case with the 
true ants, and that in this way males and females from different nests 
may pair, and thus the danger of inbreeding be lessened; but 
Holmgren and others doubt that this occurs. The greater number 
of individuals comprising one of these swarms soon perish ; they fall 
victims to birds and other insectivorous animals. 

Each of the more fortunate couples that have escaped their 
enemies, find a suitable place for the beginning of a nest and become 
the founders of a new colony. Such a pair are commonly laiown as 
the king and the queen of the colony; they are also known as the 
primary royal pair to distinguish them from the second reproductive 
caste. The primary royal pair can be recognized by the presence on 
the thorax of the stumps of the wings that they have shed. 

After the nest has been begim, the abdomen of the female becomes 
greatly enlarged, as a result of the growth of the reproductive 
organs and their products; this is greater in certain exotic species 
than it is in those fotmd in this country. Figure 311 represents 



276 



AN INTRODUCTION TO ENTOMOLOGY 




Pig 



_ 3 I I •— 
Queen ter- 
mite, Ter- 
mes gilvus. 



in natural size the queen of a species found in India. The dark spots 
along the niiddle of the dorsal wall of the abdomen 
are the chitinized parts of that region; the lighter 
portions are made up of the very much stretched 
membrane uniting the segments. This queen is a 
comparatively small one ; in some species the queens 
become from 150 to 200 vcwa. in length; of course 
such a queen is incapable of locomotion, but lives 
with its mate inclosed in a royal chamber ; their food 
is brought to them and the eggs are carried away by 
workers. In our native species the queens do not 
become so greatly enlarged and do not lose the power 
of movement. 

A remarkable peculiarity in the habits of termites 
is that the association of the male and the female is 
a permanent one ; the king and the queen live together 
in the nest, and there is repeated coition. 

The second reproductive caste. — There are fre- 
quently fotmd in the nests of termites neoteinic 
sexual forms; that is, individuals which are sexually 
mature but which retain the nymphal form of the 
body, having short wing-buds which do not develop 
further. These individuals constitute the second 
reproductive caste, which is represented by both males 
and females. The members of this caste are pale in 
color; their compound eyes are only slightly pig- 
mented; and they never leave the nest unless by subterranean tun- 
nels. If a primary king or queen dies, its place is taken by individuals 
of the second reproductive caste. For this reason, the members of 
this caste are commonly known as substitute kings and queens or as 
complemental kings and queens. The substitute 
queens produce comparatively few eggs, and conse- 
quently it requires several of them to replace a pri- 
mary queen. Many pairs of substitute kings and 
queens are commonly found in orphaned nests. 
The third reproductive caste. — In some cases there 
have been found adult neoteinic sexual forms which 
resemble workers in lacking wing-buds. These are 
known as ergatoid kings and queens. 

The workers. — If a termite nest be opened at any 
season of the year there will be found a large number 
of wingless individuals of a dirty white color, usually 
blind, and of the form represented by Figure 312. 
These are named the workers, for upon them devolve 
nearly all of the labors of the colony. A study of the internal anatomy 
of workers has sho\\-n that both sexes are represented in this caste; 
the reproductive organs are, however, only little developed as a rule; 
but occasionally workers capable of laying eggs are fotmd. The 
worker caste is not always present; it is absent in the genera Kalo- 




Fig. 312, 
worker. 



ISOPTERA 



277 




-A sol- 



tennes and Cryptotermes, where the nymphs of the reproductive forms 
apparently attend to the duties of workers; and in the genera 
Termopsis and Neotermes ordinary sterile workers are not found, but 
the third reproductive caste, large, worker-like, grayish brown, fertile 
forms, with no wing-buds, is present. The nymphs of this caste often 
perform the duties of the workers (Banks and Snyder '20). In some 
tropical species there are two types of workers, which 
differ in size. 

The soldiers. — ^Associated with the workers, and 
resembling them in color and in being wingless, there 
occur numerous representatives of another caste, 
which can be recognized by the enoimous size of their 
heads and mandibles (Fig. 313); these are the sol- 
diers. They are so named because it is believed that 
their chief "function is the protection of the colony; 
but they do not seem to be very effective in this. 
Among the soldiers, as among the workers, both sexes 
are represented ; but as a rule the reproductive organs 
are not functional. Sometimes, however, soldiers 
capable of laying eggs are found. In the genus Fig-. 3i3- 
Kalotermes soldiers with small wing-buds are often ^^'^^• 
foimd. The soldier caste has not been ioxm&mthe germs, Anoplotenncs, 
and in the genera Constrictotermes and Nasutitermes the soldier caste 
is wanting unless the nasuti, described in the next paragraph, are 
regarded as soldiers. In certain tropical species there 
are two types of soldiers which differ in size. 

The nasuti. — In certain species of termites there 

are found individuals in which the head is elongated 

into a nose-like process, from the tip of which a fluid 

^, exudes, which is used as a means of defense and also, 

1^^^ it is said, as a cement in constructing the nest and 
y^^^ the earth-like tubes through which the insects travel 

(Fig. 314). Such individuals are known as nasuti. 
In this caste the mandibles are small, differing greatly 
from those of soldiers . The nasuti are usually smaller 
than the workers and are pigmented. They have 
been commonly described as a special type of soldiers ; 
but it seems better, in order to avoid confusion, to 
regard them as constituting a distinct caste. Among 
the North American termites, nasuti are found in 
the genera Constrictotermes and Nasutitermes, which 
lack the true soldier caste. In some tropical termites two types of 
nasuti, large and small, have been found. 

As to the origin of the different castes of termites there has been 
much discussion and two radically different views are held. The 
first view was probably suggested by the well-known fact that, in the 
case of the honey-bee, queens can be developed from eggs or young 
larvcE that ordinarily would produce workers. According to this view 
the newly hatched termites are not differentiated into castes; but 




Fig. 314. — A nas- 
utus. (Aftei 
Sharp.) 



278 AN INTRODUCTION TO ENTOMOLOGY 

this differentiation takes place later as the result of extrinsic factors, 
such as food, the presence or absence of parasitic protozoa in the 
alimentary tract, and the care received from the older workers. 
According to the second view the yoimg of the different castes are 
different and the castes are therefore "predetermined in the egg or 
embryo by intrinsic factors." 

Some comparatively recent investigations support the second view. 
It was fotmd by Thompson ('17 and '19) that although the newly 
hatched nymphs are externally all alike, they are differentiated by 
internal structural characters into two clearly defined types: first, 
the reproductive or fertile forms, with large brain and large sex organs, 
and usually a dense opaque body; and second, the worker-soldier or 
sterile forms, with small brain and small sex organs, and usually a 
clear transparent body. 

It was also foimd by Thompson that later, when the nymphs had 
become from 2 mm. to 3 mm. in length, they were differentiated into 
"small-headed" but large-brained reproductive forms, and "large- 
headed" but small-brained worker-soldier forms. In the case of 
worker-soldier nymphs oiEutermes pilifrous, a Jamaican species, which 
were 2 mm. long and externally all alike, they were distinguishable, 
after staining, into worker nymphs with a small vestigial frontal 
gland, and soldier n3miphs with a large frontal gland. 

In a study oi Reticulitermes (Leucotermes)flavipes , Thompson ('17) 
foimd that the nymphs of the reproductive forms that are only 1.3 
to 1.4 mm. in length are differentiated into two groups by differences 
in the size of the brain and sex organs. These are early instars of 
the first reproductive caste and the second reproductive caste, respec- 
tively. The early instars of the third reproductive caste have not 
been distinguished from the nymphs of workers. 

There is space here for but little regarding the nest-building habits 
of these wonderful insects. In the tropics certain species build nests 
of great size. Some of these are moimds ten or twelve feet or more 
in height. Other species build large globular masses upon the trunks 
or branches of trees or upon other objects. Figure 315 represents 
such a nest which I observed on a fence in Cuba. Owing to the 
delicacy of their cuticula and the consequent danger of becoming 
shri\^eled if exposed, the termites build covered wa3''S from their 
nests to such places as they wish to visit, if they are in exposed 
situations like that shown in the figure. These exposed nests are 
composed chiefly of the excreted undigested wood upon which the 
insects have fed. This is molded into the desired form and on drying 
it becomes solid. 

The termites that live in the United States do not build exposed 
nests; and, as the queens do not lose the power of movement, there 
is no permanent royal cell, centrally located, in which the king and 
queen are imprisoned, as is the case with many tropical species. 
Some of our species mine in the earth, their nests being made under 
stones or other objects lying on the ground; some burrow only in 



I SOFTER A 



279 



wood; and others that burrow in the ground extend their nesfs into 
wood. To the last category 
belong the species of the genus 
Reticulitermes, which includes 
all of the termites found north 
of Georgia and east of Nevada. 
These often infest the founda- 
tion timbers of buildings, floor- 
ing in basements, and other 
woodwork of buildings and 
furniture. These pests will 
feed upon almost any organic 
matter; books are sometimes 
completely ruined by them. 
In infesting anything com- 
posed of wood, they eat out 
the interior, leaving a thin film 
on the outside. Thus a table 
may appear to be sound, but 
crumble to pieces beneath a 
slight weight, entrance having 
been made through the floor of 
the house and the legs of the 
table. 

While termites infest 
chiefly dead wood, there are 
many records of their infesting 
living plants. I found them 
common throughout Florida, 
infesting orange-trees, guava- 
bushes, pampas-grass, and su- 
gar-cane. When termites in- 
fest living plants, they attack that part which is at or just below the 
surface of the ground. In the case of pampas-grass the base of the 
stalk is hollowed; with woody plants, as orange-trees and guava 
bushes, the bark at the base of the tree is eaten and frequently the 
tree is completely girdled; with sugar-cane the most serious injury 
is the destruction of the seed-cane. 

Certain African termites have been found to cultivate fungus- 
gardens in their nests, similar to those of the well-known leaf-cutting 
ants. 

The care of the young and of the queens by the workers in colonies 
of social insects has attracted the attention and admiration of observ- 
ers in all times. This care has been quite generally attributed to 
something resembling the parental feelings of our own species. But 
the observations of several naturalists in recent years have sho\vn 
that with the social insects the devotion of the workers to the brood 
and to the queen is far from being purely altruistic; that it is largely 
or entirely due to a desire to feed upon certain exudates produced by 




Fig- 315- — Nest of a Cuban termite. 



280 AN INTRODUCTION TO ENTOMOLOGY 

the individuals that are fed; the feeding of the young and the queens 
being accompanied by a Hcking of their bodies by the nurses. 

Among the more important papers on this subject are one on 
termites by Hokngren ('09) and one on ants by Wheeler ('18). 
Holmgren shows that all of the castes of termites, but especially the 
queens, have extensive exudate tissues, consisting of the peripheral 
layers of the abdominal fat-body, the products of which pass through 
pores in the cuticula, where they are licked up by other members ^/i 
the colony; and that the intensity of the licking and feeding of fi^Q 
individuals of a termite colony is directly proportional to the amount 
of their exudate tissue. Wheeler in his paper on ants shows that the 
larvae of certain species of ants possess remarkable exudate organs, 
and proposes for this exchange of nourishment the term trophallaxis* 

It is believed by the writers quoted above and by others that this 
exchange of nourishment between those individuals that feed and 
those that are fed was the source of the colonial habit in social insects. 
Roubaud ('16) in a paper on the wasps of Africa points out the 
probable steps by which the social habit was developed in wasps. 
Beginning with certain solitary eumenids that feed their larvs from 
day to day and while doing this feed upon saliva exuded by the larvae, 
he suggests that there naturally follows a tendency to increase the 
number of larvae to be reared simultaneously in order at the same 
time to satisfy the urgency of oviposition and to profit by the greater 
abundance of the secretion of the larvae. 

Now that this explanation of the origin of the social habit has 
been suggested, it, doubtless, will be much discussed. The student is 
urged, therefore, to consult the current literature for opinions regard- 
ing it. 

The most extended accoimt of the termites of this country is the 
recently published paper by Nathan Banks and Thomas E. Snyder 
('20). In the first part of this paper, Mr. Banks gives a revision of 
the nearctic termites, in which all of our known species are described, 
seventeen, of them for the first time. This brings the total nimiber 
of our known species up to thirty-six, representing ten genera. 

In the second part of this paper, Mr. Snyder brings together the 
known data regarding the habits and distribution of the termites of 
the United States; much of which data is based on his personal 
observations. 

Many species of insects live in the nests of termites. The relations 
of the termitophiles, of which several hundred species have been 
described, to their hosts vary greatly; some are predatory, some are 
parasites, and others are guests. Among the guests some are indift'er- 
ently tolerated, while others are true guests which produce exudates 
that are eagerly devoured by their hosts and in return either receive 
regurgitated food or manage to prey on the defenseless brood. 
Among the termitophiles are some that are very remarkable in form, 
having the abdomen excessively enlarged and being furnished with 
large exudate organs. 

*Trophallaxis : trophe (rpocpri), nourishment; allattein (dWdrTeiv) , to exchange. 



CHAPTER XI 

Order NEUROPTERA* 

The Horned Corydalus, the Lacewing-Flies, the Ant-Lions, 
and others 

The members of this order have four wings; these are membranous 
and are usually furnished with many veins and cross-veins. In most 
members of the order, the wings have been specialized by the addition in 
the preanal area of many supernumerary veins of the accessory type. 
The mouth-parts are formed for chewing. The tarsi are five-jointed. 
The cerci are absent. The metamorphosis is complete. 

The order Neuroptera as now restricted differs greatly in extent 
from the Neuroptera of the early entomologists. Formerly there were 
included in this order many insects that are no longer believed to be 
closely related. This has resulted in the establishment of several dis- 
tinct orders for the insects that have been removed from the old 
order Neuroptera. This fact should be kept in mind when consulting 
the older text-books. 

The wings of the Neuroptera are membranous and usually fur- 
nished with many wing-veins. The two pairs of wings are similar 
in texture and usually in outline ; in some the fore wings are sHghtly 
larger than the hind wings, in others the two pairs of wings are of the 
same size. The anal area is small in both fore and hind wings ; it is 
rarely folded (Sialidce), and then only slightly so. A distinct anal 
furrow is rarely developed. Definitive accessory veins are usually 
present, and, as a rule, there are many marginal accessory veins. 
Intercalary veins are never developed. When at rest, with few ex- 
ceptions, the wings are folded roof-like over the abdomen. In some 
cases organs for uniting the fore and hind wings are present. 

Correlated with the extensive development of accessory veins in 
the Neuroptera, there has resulted in nearly all of the families of this 
order the production of a pectinately branched radial sector; that is, 
this vein is so modified that it consists of a supporting stem upon 
which are borne a greater or less number of parallel branches. This 
is shown in most of the figures of wings illustrating this chapter, 
and is a distinctive characteristic of this order; in no one of the 
other orders of living insects in which accessory veins occur is a well- 
developed pectinately branched radial sector found. Such a radial 
sector existed, however, in many of the Paleozoic insects. In certain 
genera of the Neuroptera a dichotomously branched radial sector has 
been retained. 

In many Neuroptera one or more series of cross-veins extend 
across the wing and form with sections of the longitudinal veins that 

*Neur6ptera: neuron (vevpov), a nerve; pteron (irrepSv), a wing. 
(281) 



28i 



AN INTRODUCTION TO ENTOMOLOGY 



they connect a very regular zigzag line ; such cross-veins are termed 
gradate veins. Examples of series of gradate veins are well shown in 
the wings of the Hemerobiidse and in those of the allied families. 
The mouth-parts are formed for chewing. In several families the 
larvae suck the blood of their prey by 
means of their peculiarly modified man- 
dibles and maxillae. These are very long 
and those of each side form an organ for 
piercing and sucking. The mouth-parts 
of the larva of an ant-lion will serve to 
illustrate this type of mouth-parts (Fig. 
316). 

In this insect the mandibles (md) are 
very long, curved at the distal end, fitted 
for grasping and piercing the body of the 
prey, and armed with strong spines 
and setae. On the ventral aspect of each 
mandible there is a furrow extending the 
entire length of the mandible; and over 
this fvirrow the long and slender maxilla 
(mx) fits. On the dorsal aspect of the 
maxilla there is also a furrow. These two 
furrows form a tube which extends from 
the tip of the combined mandible and 
maxilla to the base of this organ where it 
communicates with the mouth cavity. 
Through this tube the blood of the prey 
is conveyed to the mouth. On the middle 
line of the body, between the mentum (m) 
and the front margin of the dorsal wall of 
the head (/), there is a tightly closed slit 
which is the mouth ; this, however, is not 
functional, the food being received into 
lateral expansions of the mouth-cavity at 
the base of the mandibles and maxillce. 
For a more detailed account of the struc- 
ture of the mouth-parts of an ant-lion, see Lozinski ('08). 

The metamorphosis is complete. The larvae that are known are 
predacious or parasitic and in most cases are campodeif orm ; a few 
of them are aquatic, Sialidae, Sisyridae, and certain exotic forms, but 
most of them are terrestrial ; some when full-grown enter the ground 
and make earthen cells in which they transfonn, but most of them 
spin cocoons. The silk of which these cocoons are made, in the case 
of those in which the silk-organs have been described, is secreted by 
modified Malpighian vessels and is spun from the anus. 

The silk-organs of Sisyra will serve as an example of neuropterous 
silk-organs; these were described by Miss Anthony ('02). Figure 317 
is a diagram of a sagittal section of a larva through the median plane. 
In this larva the posterior fourth of the mid-intestine is merely a 




Fig. 316. — Head and mouth- 
parts of a larva of an ant- 
lion, ventral aspect: c, car- 
do of the maxilla ;e, eye;/, 
front margin of the dorsal 
wall of the head, labrum 
(?); m, mentum; wc?, man- 
dible, mx, maxilla; p, la- 
bial palpus; s, stipes of the 
maxilla. 



NEUROPTERA 283 

solid cord of atrophied cells; the passage from the mid-intestine to 
the hind-intestine is thus closed. The atrophied part of the mid- 
intestine ends in the walls of a dilation, the silk-receptacle {sr). 
Into this receptacle empty the five Malpighian tubes, three of which 
are attached by both ends and two of which extend posteriorly and 
end free in the body cavity; all are modified in their middle portions 
for the secretion of silk; here the cells are much larger and more 
irregular in shape than the ordinary Malpighian tubule cells, and 
show singular, branched nuclei lilce those characteristic of silk-gland- 




Fig. 317. — Sagittal section of a larva of Sisyra: a, b~b', c-c', three silk-glands 
attached at both ends; d, e, two silk-glands attached at one end; sr, silk- 
receptacle; sp, spinneret; /, fat-bodies; br, brain; g, suboesophageal ganglion; 
r, band of regenerative cells of the stomach ; p, point of junction of sucking 
tubes; s, sucking pharynx ; m, muscle attachment of pharynx; 0, oesophagus. 
(From Anthony.) 

cells of caterpillars and other insects. That part of the hind-intestine 
extending back from the silk-receptacle is a slender tube for the 
greater part of its length; but in the last three abdominal segments 
it is enlarged, forming a reservoir for accumulated silk (sp), which 
is spun from the anus when needed for making the cocoon. 

The pupaj of Neuroptera are exarate, that is, their legs and wings 
are free. In some cases (Chrysopa, Hemerobius, and Mantispa) the 
pupa crawls about for a time after leaving its cocoon and before 
changing to the adult. 

The known Neuroptera of the world represent twenty families; 
the wings of one or more members of each of these families have been 
figured by the writer in his "The Wings of Insects." Thirteen of 
these families are represented in North America; these can be sepa- 
rated by the following table. 

TABLE OF THE FAMILIES OF NORTH AMERICAN NEUROPTERA 

A. Prothorax as long as or longer than the mesothorax and metathorax com- 
bined. 
B. Fore legs greatly enlarged and fitted for grasping, p. 289. Mantispid^ 
BB. Fore legs not enlarged and not fitted for grasping, p. 289. Raphidiid^ 
AA. Prothorax not as long as the mesothorax and metathorax combined. 

B. Hind wings broad at base and with the anal area folded like a fan when 

not in use. p. 284 SiALlD^ 

BB.Hind wings narrow at base and not folded like a fan when closed. 

C. Wings with very few veins and covered with whitish powder, p. 307. 

CONIOPTERYGIDAE 

CC. Wings with numerous veins and not covered with powder. 

D. Antennae gradually enlarged towards the end or filiform with a 
terminal knob. 



284 ^A^ INTRODUCTION TO ENTOMOLOGY 

E. AntenriEe short; wings with an elongate cell behind the point 

of fusion of veins Sc and Rj. p. 303 MYRMELEONlDiE 

EE. Antennas long; wings without an elongate cell behind the 

point of fusion of veins Sc and Ri. p. 305 Ascalaphid^ 

DD. Antennae not enlarged towards the end. 

E. Male with pectinate antennae; female with an exserted 

ovipositor, p. 297 Dilarid^ 

EE. Antennae not pectinate in either sex; fenaale without ex- 
serted ovipositor. 
F. Radius of the fore wings with apparently two or more 
sectors. 
G. Radius of the fore wings with apparently two sectors, 
one of which is vein R2 +3 and the other veinR4-l-5. 

p. 293 S\MPHEROBIID/E 

GG. Radius of the fore wings with three or more sectors. 
Veins R4 and Rj arise separately from vein Rj; 
one or more definitive accessory branches of the 
radius of the fore wings present, p. 294 

HEMEROBIIDiE 

FF. Radius of the fore wings with a single sector. 

G. Radial sector of the fore wings without definitive 
accessory veins although marginal accessory 

veins are present, p. 291 Sisyrid^ 

GG. Radial sector of fore wings with definitive ac- 
cessory veins. 
H. Transverse veins between the costa and sub- 

costa simple, p. 299 CHRYSOPIDyE 

HH. Many of the transverse veins between the 
costa and subcosta forked. 

I . Humeral cross- vein recurved and branch- 

ed; first radio-medial cross-vein of the 
hind wings longitudinal and sigmoid. 

p. 298 POLYSTCECnOTID^ 

II. Humeral cross- vein not recurved; first 
■ radio-medial cross-vein of the hind wings 

transverse, p. 298 BEROTHlDiE 

Family SIALID^* 
The Sialids 

The members of the Sialidce differ greatly in size and appearance; 
but they agree in having the hind wings broad at the base with the 
anal area folded like a fan when not in use. In this respect they 
differ from all other Neuroptera. 

The t3^pe of the wing-venation of the sialids differs greatly in the 
two subfamihes into which the family is divided, as described below. 

The larv'as are aquatic, predacious, campodeiform, and possess 
paired, lateral filaments on most or on all of the abdominal segments. 
They leave the water when full-growTi and transform in earthen cells 
on the banks of the streams or lakes in which the}' lived as larvae. 
The eggs are deposited in clusters on any convenient support near 
the water, in such situations that the young lar\'^ can easily find 

*This family is separated from the Neuroptera by Handlirsch ('o6-'o8) as a 
distinct order, the Alegaloptera. H. W. Van der Weele Cio) also separates it 
from the Neuroptera, but he associates with it the family Raphidiidae in his order 
Megaloptera. 



NEUROPTERA 



28.- 



access to the water. The adults fly but little; they are most often 
found resting on some support near the water, with the wings folded 
over the abdomen. 

The Sialidse of the world have been monographed by H. W. 
Van der Weele Cio). 

The family vSialidae is divided into two subfamilies; these can be 
separated as follows : 

A. Ocelli wanting; fourth tarsal segment prominently bilobed; radial sector 
not pectinately branched. Insects rather small, having an expanse of 
wings of about 25 mm. p. 285 Sialin^e 

A.-\. With three ocelli; fourth tarsal segment simple, not bilobed; radial sector 
pectinately branched. Insects large or moderately large, p. 286 

CORYDALIN.« 

Subfamily ^lALl^JE 
The Alder-Flies 

The alder -flies are so-called because the adults are commonly 
found on alders on the banks of streams; this name was given to 
them by English anglers. 

The subfamily Sialinae includes only two genera, both of which 
are represented in this coimtr>% each by a single species. These 
genera are distinguished as follows : 

A. Costal area of the fore wings greatly expanded before the middle (Fig.3i8j. 

SlALIS 

AA. Costal area of the fore wings slightly expanded before the middle 

Protosialis 




Fig. 318. — Wings of Sialis infumata. 



286 



AN INTRODUCTION TO ENTOMOLOGY 



The smoky alder-fly, 5iafo injumdta. — This is a small insect hav- 
ing a wing-expanse of about 2 5 mm. ; the males are sometimes smaller 
than this, and the females slightly larger. It is dusky brownish in 
color. It can be easily recognized by the form and venation of its 
wings (Fig. 318). 

The costal area of the fore wings is greatly expanded before the 
middle, and most of the wing-veins are stout. A striking feature of 
these wings, one that is characteristic of the subfamily Sialinae, is 
that the radial sector is nearly typical in form; the only modification 
being the development of one or more marginal accessory veins upon 
it. These accessory veins, however, are in a quite different position 
from that occupied by the accessory veins borne by the radial sector 
in the Corydalinse, where a pectinately branched 
radial sector has been developed. 

The larva (Fig. 319) is furnished with the paired 
lateral filaments characteristic of the larvce of the 
Sialidas on the first seven abdominal segments. These 
filaments are more or less distinctly five-segmented. 
The last abdominal segment is prolonged into a taper- 
ing lash-like filament. 

The larvas are found in swiftly flowing streams 
adhering to the lower side of stones in the bed of the 
streams and in trashy places filled with aquatic plants 
in the borders of streams and ponds; they are very 
active. The larvae transform in earthen cells at some 
little distance from the water. Two or three weeks 
after the making of the pupal cell the adult fly 
emerges. 

The eggs are laid in patches, each consisting 
of a single layer of eggs. The females frequently 
add their eggs to patches of eggs that have been laid 
by other females. The eggs when first laid are 
lighter in color than later. 

Several specific names have been given to what 
are now believed to be merely varieties of this 
species. 
Protoslalis americana. — In this species the costal area of the fore 
wings is only slightly expanded before the middle; and the wing- 
veins are not as stout as in Sialis. The early stages have not been 
described. 




Fig. 319. — Larva 
of Sialis inju- 
mata. (After 
Needham.) 



Subfamily CORYDALIN^ 

Corydalus and the Fish-Flies 

The subfamily Corydallnas is represented in this country by the 
well-known homed coiydalus and several smaller species, commonly 
known as the fish-flies. In these insects there are three ocelli; the 
fourth tarsal segment is not bilobed; and the radial sector is pec- 
tinately branched (Fig. 320). The larvae are distinguished by the 



NEUROPTERA 



287 



presence of a pair of anal prolegs, each of which bears a pair of hooks. 
Six species are found in the United States and Canada; these repre- 
sent four genera, which can be separated as follows. 
A. Latero-caudal angles of the head with a sharp tooth. Large insects, p. 287 

CORYDALUS 

AA. Latero-caudal angles of the head unarmed. Insects moderately large; the 
fish-flies. 
B. Wings somewhat ashy in color with more or less dusky markings. 

C. Veins of fore wings marked with dark and light, uniformly alternate. 

p. 288 Chauliodes 

CC. Veins of fore wings uniform in color except where dusky markings 

cross them. p. 288 Neohermes 

BB. Wings black or brown with white markings, p. 288 Nigronia 

Corydalus. — The only member of this genus in our fatma is 
Corydalus cornutus. This is a magnificent insect, which has a wing- 
expanse of from 100 to 130 mm. Figure 321 represents the male, 




jcf^ 2d A Cui Cuia 

Fig. 320. — Fore wing of a pupa of Corydalus. 

which has remarkably long mandibles. The female resembles the 
male, except that the mandibles are comparatively short. 

The larv^ are called dobsons or hellgrammttes by anglers and 
are used by them for bait, especially for bass. Figure 322 represents 
a full-grown dobson, natural size. These larvae live under stones in 
the beds of streams. They are most abrmdant where the water flows 
swiftest. They feed upon the naiads of stone-flies and May-flies and 
on other insects. 

The larvas of Corydalus dift'er from those of the following genera 
in the possession of a tuft of hair-like tracheal gills at the base of 
each of the lateral appendages on the first seven abdominal segments. 

When about two years and eleven months old, the larva leaves 
the water and makes a cell under a stone or some other object on 
or near the bank of the stream. This occurs during the early part 
of the summer ; here the larva changes to a pupa. In about a month 
after the larva leaves the water, the adult insect appears. The eggs 
are then soon laid; these are attached to stones or other objects 
overhanging the water. They are laid in blotch-like masses, which 
are chalky white in color and measure from 12 mm. to nearly 25 mm. 
in diameter. A single mass contains from two thousand to three 
thousand eggs. When the larvas hatch they at once find their way 
into the water, where they remain imtil full-grown. 



288 



AN INTRODUCTION TO ENTOMOLOGY 



Chauliodes. — See the table on page 287 for the discinguishing 
characteristics of this genus. There are two species in our fauna; 
these are distinguished as follows: 

Chauliodes rastricornis. — In this species the antennas are serrate; 
the embossed markings on the head and prothorax are black on a 
paler groimd; and the prothorax is longer than wide. 





Fig. 322. — Larva of 
Corydahis. 



Fig. 321. — Corydalns coniiUus, male. 



Chauliodes pectinicornis . — In this species the antennae are serrate; 
the embossed markings on the head and prothorax are yellow on a 
black groimd; and the prothorax is not longer than wide. 

Neohennes. — This genus is represented by Neohermes caHformcus. 
In addition to the characters given in the table of genera above, this 
species is distinguished by the great length of its antenna, which are 
about two-thirds as long as the fore wings. 

Nigronia. — In this genus the wings are black or brown with white 
markings. Two species only are knowm; these can be distinguished 
by the form of the white markings on the wings. 

Nigronia fascidtus. — In this species there is a continuous, broad, 
somewhat arcuate, white band extending across the middle of each 
wing and almost attaining the hind margin. 

Nigronia serricornis. — In this species there is an irregular band of 
white spots, generally broadest in front, extending across the middle 



NEUROPTERA 



289 



of each front wing. On the hind wings, the white band is representee^ 
by only a few minute dots or is entirely wanting. 



Family RAPHIDIID^* 



The Snake-Flies 



Fig. 323.^ — Raphidia, 
female. 



The members of the RaphidiidcC are found in this country only 
in the Far West. They are strange-appearing insects, the prothorax 
being greatly elongate, like the neck of a camel 
(Fig. 323). The female bears a long, slender, 
sickle-shaped ovipositor at the end of the ab- 
domen. The fore legs resemble the other pairs 
of legs, and are borne at the hind end of the pro- 
thorax. The wings are long and narrow and fur- 
nished with a pterostigma. 

The wing-venation of a representative of each of the two genera 
belonging to this family is figured by the 
writer in his "The Wings of Insects." 

The larvce are found under bark and 
are carnivorous. They are common in Cali- 
fornia imder the loose bark of the eucalyp- 
tus. They also occur in orchards, and 
doubtless do good by destroying the larvae 
and pupae of the codlin-moth. The pupas 
are not enclosed in silken cocoons but lie 
concealed in sheltered places. Figure 324 
represents a larva and a pupa of Raphtdia 
as figured by Professor Kellogg. 

This family includes only two genera, 
Raphidia and Inocellia. In the former there 
are three ocelli on the top of the head be- 
Fig._ 324.— Larva^and pupa tween the compound eyes ; in the latter these 
ocelli are waa'ting. Six species of Raphidia 
and three of Inocellia are found in America 
north of Mexico. 




of Raphidia. (From Kel- 
logg.) 



Family MANTISPID^ 
The Mantis-like Nenroptera 

The members of the Mantispida) are even more strange in appear- 
ance than are those of the preceding family. Here, as in that family, 

*This family is separated from the Neuroptera by Handlirsch ('o6-'o8 ) and 
• "aade to constitute a separate order, the Raphidioidea. 



290 



AN INTRODUCTION TO ENTOMOLOGY 



the prothorax is greatly elongated ; but the members of this family can 

be easily recognized by their re- 
markable fore legs, which are great- 
ly enlarged and resemble those of 
the praying mantes in form (Fig. 
325). These legs are fitted for seiz- 
ing prey; and, in order that they 
may reach farther forward, they are 
joined to the front end of the long 
prothorax. In the adult stage, 
these insects are predacious; while 
the larvae, so far as is known, are 
parasitic. 

Brauer ('69) described the trans- 
formations of Mantispa styriaca, a 
European species. This insect 
undergoes a hypermetamorphosis. 
It was accidentally discovered that the larvffi were parasitic in the 
egg-sacs of spiders of the genus Lycosa. These are the large black 




Fig. 325. — Mantispa. In the speci- 
men figured the fore legs were 
twisted somewhat in order to 
show the form of the parts. 




Fig. 326. — ^Hypermetamorphosisof ilfaw.'i5/?a. (From Henneguy, after Brauer.) 



spiders which are common tinder stones, and which carry their egg-sacs 
with them. Brauer obtained eggs from a female Mantispa kept in 
confinement. These eggs were rose-red in color, and fastened upon 
stalks, like the eggs of Chrysopa. The eggs were laid in July; and 
the larvfe emerged 2 1 days later. The yoimg larvee are campodeiform 
(Fig. 326, A); they are very agile creatures, with a long, slender 
body, well-developed legs, and long, slender antennas. They pass the 
winter without food. In the spring they find their way into the egg- 
sacs of the above-nam.ed spiders. Here they feed upon the yotmg 
spiders; and the body becomes proportionately thicker. Later 
the larva molts and undergoes a remarkable change in form, becom- 
ing what is known as the second larva; in this stage the larva is 



NEUROPTERA 291 

scarabeiform (Fig. 326, B); the legs are much reduced in size; the 
antenna are short ; and the head is very small. When fullv grown this 
larva measures from 7 to 10 mm. in length. It then spins a cocoon, 
and changes to a pupa within the skin of the larva. Later the larval 
skin is cast; and, finally, after being in the cocoon about a month, 
the pupa becomes active, pierces the cocoon and the egg-sac, and 
crawls about for a time (Fig. 326, C) ; later it changes to the adult 
form (Fig. 326, D). 

The life-history of Symphasis vdria, a Bradlian species, is partly 
known. The larv£e of this species live parasiticallv i 1 the nests of 
wasps; when full-grown each larva spins a cocoon "in one of the cells 
of the nest. 

Only a few representatives of this family occur in the United States, 
and all are rare insects. 

Family SISYRID^ 
The Spoil gilla-Flies 

The Sisyridce in- 
clude a very limited 
number of small, 
smoky brown insects, 
of the form shown in 
Figure 327. They are 
called Spongilla-jiies 
because the larvae live 
as parasites in fresh- 
water sponges, the 
typical genus of which is Spongilla. Two interesting features of these 
insects are the comparative simplicity of the wing-venation of the 
adults, and the anomalous habits of the larvae. 

The more striking characteristics of the wings (Fig. 3 28) are the 
following : The costal area of the fore wings is not greatly broadened ; 
the humeral vein is not recurrent and is not branched. Veins Sc and 
Ri coalesce near the apex of the wing. The radial sector is pectinately 
branched; but no definitive accessory veins have been developed; 
this is the simplest form of pectinately branched radial sector foimd 
in the fore wings in this order. Marginal accessory veins are present. 

The larvce are aquatic and live in fresh-water sponges, upon 
which they feed. The life-history of a representative of each of the 
two genera, Sisyra and Climacia, which constitute this family, was 
worked out by Professor Needham ('01); and the anatomy and 
transfonnations of a species of Sisyra were carefully studied by Miss 
Anthony ('02). The following notes are based on the accounts 
published by these authors. 

Sisyra mnbrdta. — The form of the adult is shown in Figure 327; 
its color is nearly unifoiTn blackish brown. The legs and the apex 
of the abdomen are dirty 3'ellowish. The length of the male to the 
tips of the wings is 6 mm ; that of the female, 8 mm. 




Fig. 327. — Sisyra nmbrata, greatly enlarged. (From 
Anthony.) 



292 



AN INTRODUCTION TO ENTOMOLOGY 



The larva (Fig. 329) is campodeiform. Its mouth-parts are 
formed for sucking as in the larvcC of ant-Hons (see page 282) ; they 




Fig. 328. — Wings of Sisyra flavicornis . 

are very long; and two sucking organs, each formed of the mandible 
and maxilla of one side, are closely parallel for the greater part of 
their length. Each of the first seven abdominal segments bears on 
the ventral side a pair 
of jointed filaments 
which are believed to 
be tracheal gills. 
When full-grown, the 
larva leaves the water 
and spins over itself, 
on some object near 
the water, a hemi- 
r;pheric cover of close- 
ly woven silk, at- 
tached by its edges to 
the supporting surface, 
and a complete inner 
cocoon of consider- 
ably smaller size, like- 
wise closdy Vv^oven. 

The silk-organs of the larva are described 
on pages 282-3. 

Climdcia dictyona. — This species resem- 
bles the preceding in size but is yellowish 





Fig. 330. — Cocoon and 
cocoon-cover of Cli- 
macia. 



Fig. 329. — Larva of Sisy- 
ra umbrata. (After An- 
thony.) 



NEUROPTERA 



293 



in coloration ; the two can be distinguished by the form of the labia 
(Fig. 331). 

In the larva of this species the setae on the dorsum of the tho- 
rax are situated on tubercles; they are sessile in the larva of 5^5 jra. 
The habits of the larva are similar to those of Sisyra. 




Fig. 331. — Labia of Spongilla-flies: a, Climacia dictyona; h, Sisyra umbrata. (After 

Needham.) 

Before spuming its cocoon this larva spins a hemispheric cover 
beneath which the cocoon is made, as does the larva of Sisyra. But 
in the case of Climacia this cocoon-cover is lace-like; it is a beautiful 
object (Fig. 330). 

Excepting the sialids, the larva of Sisyra and Climacia are the 
only known aquatic neuropterous larva? foimd in this country. 



Family SYMPHEROBIID^ 
The Sympherohiids 

This family includes certain insects which were formerly classed 
with the Hemerobiida? but which exhibit a type of specialization of 
the wings that is quite different from that which is distinctively 
characteristic of that family. 

The distinctive characteristic of the Sympherobiidas is that vein 
R2+.3 of the fore wings has become separated from the remainder 
of the radial sector and is attached separately to vein Ri. This 
results in the radius of the fore wing having two sectors, each of which 
is forked (Fig. 332). 

In this family the number of the branches of the radial sector has 
not been increased, this vein being four-branched in both fore and 
hind wings ; but the tips of all of the branches are forked. The costal 
area of the fore wing is broad towards the base of the wing; and the 
himieral vein is recurved and branched. 

The North American species of this family represent two genera. 



294 



AN INTRODUCTION TO ENTOMOLOGY 



Sympherobius. — In this genus there are two series of gradate veins 
in the fore wings; the outer series consists of four cross-veins (Fig. 332). 
Seven American species have been described. The wing-expanse of 
these insects ranges from 9 mm. to 1 2 mm. 




Fig. 332. — Wings of Sympherobius amiculus. 

Psectra. — In this genus there is only one series of gradate veins 
in the fore wings. The only species is Psectra dtptera. The specific 
name of this species was suggested by the fact that in the female the 
hind wings are atrophied. This is a widely distributed species both 
in this coimtry and in Europe. Its wing expanse is from 5 mm. to 
6 mm. 

Family HEMEROBIID^ 

The Hemer. hiids 



The Hemerobiids include insects of moderate size; in most of 
our species the wing-expanse is between 12 mm. and 22 mm.; in 
one species of Megalomus it is only 6 mm. In most of the species the 
body is brown or blackish and is often marked with yellow; in some 



NEUROPTERA 



295 



the body is pale yellow. The wings are usually hyaline or pale 
yellowish. 

This farnily has been greatly restricted in recent times ; formerly 
there were included in it the members of the two preceding and the 
three following families. 




^^^^^^^^^ 




Fig. 333. — Wings of Hemerobius humuli 

As now restricted this family is composed of a group of genera 
that are characterized by a distinctive manner of specialization of the 
radius of the fore wings. This feature is a coalescence of vein Ri and 
the stem of the pectinately branched radial sector, which results in 
what I have termed the suppression of the stem of the radial sector. 

A comparatively simple example of this condition is exhibited 
by Hemerobius humuli; in the fore wings of this species (Fig. 333), 
veins R5, R4, and R2+3 arise separately from what appears to be 
the main stem of the radius but which is really vein Ri and the basal 
part of the radial sector coalesced. 

An early stage in the suppression of the stem of the radial sector 
is shown in the hind wing oi Hemerobius humuli (Fig. 333). Here 



29G 



AN INTRODUCTION TO ENTOMOLOGY 



vein Ro+3-r4 is bent forward near its base and is joined to vein Ri. 
The extending of the union of veins Ri and R2+3+4 from the point 
where they now anastomose towards the base of the wing, so as to 
obhterate the small cell between them, and also towards the apex of 




Fig. 334.- — Wings of Megalomus mosstus. 



the wing for a certain distance, would produce the condition that exists 
in the fore wing. 

The wings of Hemerobius represent a comparatively simple type 
of hemerobiid wings; those of Megalomus mcestus (Fig. 334), a more 
complicated one. Here there have been developed a larger number 
of definitive accessory veins and of marginal accessory veins. 

Under the title "A Revision of the Nearctic Hemerobiidse" Mr.N. 
Banks ('05) has published an account of this family, the two preceding 
families, and the three following families, in which all of our species 
known at that time are described. 



NEUROPTERA 



297 



The larvas of the hemerobiids, as far as they are known, resemble 
in their general appearance aphis-lions (Chrysopidae) , and, like the 
aphis-lions, feed on 
plant-lice and other 
small insects. Their 
mouth -parts are 
formed for piercing 
and sucking (see 
page 282), and the 
posterior part of 
the alimentary ca- 
nal is transformed 
into a silk-organ, as 
in Sisyra (see page 
283). They are 
found most often 
running about on 
trees, and especial- 
ly on coniferous 
trees. Some, like 
the aphis-lions, are ^% 
naked ; but the lar- 
vae of some species, 
at least, of Hemcro- 
hius cover them- 
selves with a cloak, composed of the empty skins of their victims 
and other debris (Fig. 335). These larvae are furnished at the sides 
with projections which serve as pedicels to elongate, divergent hairs 
that help to keej^ the cloak in place. 

There are thirty described American species belonging to this 
family; these represent four genera, Hemerobius, Boriomyia, Megalo- 
mus, and Micromus. 

Family DILARIDyE 




335. — Larva of Hemerobius: A, the larva bare; 
B, the same partially concealed by the remains of its 
victims, etc.; a portion of the covering has been re- 
moved in order to show the head. (From Sharp.) 



The Dilaridse is a small family, representatives of which are found 
chiefly in the Old World. In this family the antennas of the male 
are pectinate ; and the female is furnished with an exerted ovipositor. 

Only a single, exceedingly rare species, Dllar americdnus, has been 
foimd in North America; and of this only a single female individual 
is known. This is a small insect ; the length of the body, not includ- 
ing the ovipositor, is about 3 mm.; the length of the ovipositor is a 
little greater than that of the body ; the expanse of the wings is about 
1 4 mm. There is a single five-branched radial sector in both fore and 
hind wings. In several exotic species the radius of the fore wings 
bears two or more sectors. 

The type of our species was taken at Bee Spring, Kentucky, in 
June, 1874. 



298 



AN INTRODUCTION TO ENTOMOLOGY 
Family BEROTHID^ 



The Berothidas is a small family, which is represented in Ncrth 
America by a single genus, Lomamyia, of which only two species are 




Fig. 336. — Wings of Berotha insoliia. 

known. Figure 336 represents the venation of the wings of the type 
species of the family, Berotha insolita, which is found in India, and 
to which our species are closely allied. 

The fore wings are falcate, which is not true of certain exotic genera ; 
the humeral cross-vein is not recurved ; many of the transverse veins 
between the costa and the subcosta are forked ; the radial sector bears 
definitive accessory veins; and there is a single series of gradate 
veins in the radial area. In the hind wings the first radio-medial 
cross-vein is transverse; vein Cu2 is wanting; and the area between 
the margin of the wing and veins ist A and Cui is narrow and largely 
occupied by the fanlike tips of the accessory veins. 

Nothing is known regarding the early stages of these insects. 




Family POLYSTCECHOTID^ 

The family Polystoechotidse was 
established to receive the genus 
Polystoechotes ,oi\Nh{c\\ only two species, 
both American, are known. These are 
larger insects than are the members of the allied families. 



Fig- 337. — Polystachotes puncta 
tus. 



NEUROPTERA 



299 



measuring in wing-expanse from 40 mm. to 75 mm., vars-ing greatly 
in size. They are nocturnal and are attracted to lights. The two 
species can be distinguished as follows : 

PolystoEchotes piinctdtiis (Fig. 337). This is blackish, with three 
longitudinal lines on the prothorax, and with the lateral margins of 
this segment yellowish. 




Pig. 338. — Wings of Polystcschotes punctatus. 

Polystoschotes vittdtus. — This is pale yellowish, with a black stripe 
on the sides of the thorax, and with the abdomen dark brown. 

The larva of neither of these species is known. This is a strange 
fact considering the size and the abundance of these insects. 

The wings oi Polystachotes punctatus (Fig. 338) represent the type 
of wing-venation characteristic of this family. In these wings the 
humeral cross-vein is recurved and branched; veins Sc and Ri co- 
alesce at the tip; the radial sector is pectinately branched; the nimi- 
ber of cross-veins is greatly reduced; but there is in both fore and 
hind wings a very perfect series of gradate veins. 

In these wings the development of definitive accessory veins on 
the radial sector and the regularity of the border of marginal accessory 
veins have reached a very high degree of perfection. 

Family CHRYSOPID^ 
The Lacewing-Flies or Aphis-Lions 
The family Chrysopidas includes the insects commonly known 
as lacewing-fiies; these and their larvee, the aphis-lions, are common 



300 



AN INTRODUCTION TO ENTOMOLOGY 



and well-known insects; they are found upon herbage and the foliage 

of shrubs and trees 
throughout the summer 
months (Fig. 339). 

The adults are easily 
recognized by their deli- 
cate lacelike wings and 
their green or yellowish 
green color. Members of 
several of the preceding 
families have delicate 
lacelike wings; but with 
those insects the wings 
are more or less brown or 
are hyaline. 

While these insects 
are most commonly 
known as the lacewing- 
fiies, other popular names 
have been applied to 
them; they are some- 
times called golden-eyed flies, on account of the peculiar metallic 
color of their eyes while alive; and as some species, when handled, 
emit a very disagreeable odor, they have been called stink-flies, an 
undesirable name for such beautiful insects. 

The wings of the Chrysopidse are characterized by a very re- 
markable and distinctive type of specialization, the details of which 




Fig. 339-— Eggs, 
Chrysopa. 



larva, cocoon, and adult of 




Fig. 340. — Fore wing of Chrysopa nigricornis: ]M', pseudo-media; Cui', pseudo- 
cubitus. 



can be understood only by a study of the tracheation of the wings 
of the pupas. Such a study has been made by McClendon ('06), 
Tillyard ('16), and R. C. Smith ('22). 

A superficial examination of a wing of Chrysopa (Fig. 340) reveals 
the presence of two longitudinal veins between the radial sector and 
the inner margin of the wing, one of which appears to be the media 
and the other vein Cui; but each of these, as is shown later, is a 
serial vein composed of sections of several veins. 



NEUROPTERA 



301 



As it would be impracticable to apply to these serial veins names 
indicating their composition, they have been termed the pseudo- 
media or vein M' and the pseudo-ciibitus-one or vein Cui', re- 
spectively (Fig. 340, ]\r and Cu/). 




Fig. 341. — Tracheation of the wings of a pupa of Chrysopa nigricornis. 



An examination of the tracheation of the wings of a pupa of 
Chrysopa nigricornis reveals the nature of the two serial veins M' 
and Cui' (Fig. 341). 

In order to show more definitely the composition of the two serial 
veins, a diagram of an adult wing is given (Fig. 342). in which the 
elements of the coalesced veins are represented slightly separated, 
and the cross-veins connecting the coalesced veins are represented 
by dotted lines. By comparing this diagramwith Figiire 340 the 
homologies of the different veins can be recognized. 

The larvce of the lacewing-fiies are known as aphis-lions, because 
they feed upon aphids; they are found on the foliage of plants in- 
fested by these pests; they also feed upon other small insects and 
the eggs' of insects; they are spindle-shaped (Fig. 339) and arefur- 
nished with piercing and sucking mouth-parts like those of ant-lions. 

Nearly all aphis-lions are naked; but a few species cover them- 
selves with the skins of their victims and other debris, as do the larvs 
of Hemerobius. This has l^een obser^'ed by European writers (Sharp 



302 



AN INTRODUCTION TO ENTOMOLOGY 



'95); and recently Mr. R. C. Smith ('21) has found that the larvae 
of several of our native species have a similar habit. 

The cocoons are generally found on the lower sides of leaves or 
on the supports of plants; they are spherical and composed of dense 
layers of silk. In order to emerge the insect cuts a circular lid from 




^'+^^r':^r^r^ 



Fig. 342. — Diagram of the wings of Chrysopa nigricornis, showing the coalesced 
veins slightly separated. 



one side of the cocoon ; this is done by the pupa by means of its 
mandibles. After emerging from its cocoon, the pupa crawls about 
for a short time before changing to the adult state. 

The adults are often attracted to lights at night. A remarkable 
fact in the life-history of these insects is the way in which the female 
cares for her eggs. When about to lay an egg she emits from the end 
of her body a minute drop of a tenacious substance, which is probably 
a product of the colleterial glands; this she applies to the object on 
which she is standing and then draws it out into a slender thread by 
lifting the abdomen ; then an egg is placed on the stmimit of this 
thread. The thread dries at once and firmly holds the egg in mid-air. 
These threads are usually about 12 mm. in length, and occur singly 
or in groups; a group is represented attached to a leaf in Figure 339. 

About fifty species belonging to this family have been found in 
the United States and Canada; the greater number of these belong 
to the genus Chrysopa. 



NEUROPTERA 



303 




Fig- 343- — Larva, cocoon with pupa-skin projecting, and 
adult, of an ant-lion. 



Family MYRMELEONID^ 

The Ant-Lions 

The members of the family Myrmeleonidas are commonly known 
as ant-lions. This name was suggested by the fact that the larvee of 
the best-known 
species, those that 
dig pitfalls, feed 
chiefly on ants. 

The adults are 
graceful creatures. 
The body is long 
and slender (Fig. 
343); the antenucB 
are short and en- 
larged towards the 
end ; the wings are 
long and narrow 
and delicate in 
structure ; they are 
furnished with many accessory veins, both definitive and marginal, 
and with very many cross-veins. A distinctive feature of the wings 
of these insects is the presence of an elongated cell behind the point 
of fusion of veins Sc and Ri (Fig. 344); this characteristic serves to 
distinguish this family from the closely allied Ascalaphidas. 

The determination of the homologies of the wing-veins of the 
Myrmeleonidse was completed only recently. The results of this de- 
termination are set forth in detail by the writer in his "The Wings 
of Insects," where they are illustrated by many figures. 

Our native species, as a rule, are not striking in appearance; 
the wings are hyaline and are often more or less spotted with black or 
brown marks; iDut certain exotic forms, as those of the genus Pal- 
pares, are large and have conspicuously marked wings. 

The larvae have broad and somewhat depressed bodies which 
taper towards each end (Fig. 343). The mouth-parts are large and 
powerful and are of the piercing and sucking type; they are described 
on page 282. The pupa state is passed in a spherical cocoon, made of 
sand fastened together with silk, and neatly lined with the same 
material (Fig. 343). The silk is spun from the posterior end of the 
alimentary canal and is secreted by modified Malpighian vessels, as 
in Sisyra (see page 283.) 

This is a large family including several hundred described species. 
In his "Catalogue of the Neuropteroid Insects of the United States," 
Banks ('07) lists fifty-eight species of this family known at that time 
to occur in our fauna; these are distributed among eleven genera. 

The life-histories of comparatively few of the species are known ; 
but certain species, the larvae of which dig pitfalls in sandy places, 
have attracted much attention since the earliest days of entomology. 



304 



AN INTRODUCTION TO ENTOMOLOGY 



Ant-lions are much more common in the Southern and Southwest- 
ern States than they are in the North. The pitfalls of the larvae are 
usually found in sandy places that are protected from rain, as beneath 
buildings or overhanging rocks. In making these pitfalls the sand 
is thrown out by an upward jerk of the head, this part of the body 




Fig. 344. — Wings of Myrmeleon. 



serving as a shovel. The pits dififer greatly in depth, according to the 
nature of the soil in which they are made. Their sides are as steep 
as the sand will lie. When an ant or other wingless insect steps upon 
the brink of one of these pits, the sand crumbles beneath its feet, 
and it is precipitated into the jaws of the ant-lion, which is buried 
in the sand, with its jaws at the bottom of the pit (Fig. 345). Incase 
the ant does not fall to the bottom of the pit, the ant-lion undermines 
it by throwing out some sand beneath it. I have even seen an ant-lion 
throw the sand in such a way that in falling it would tend to hit the 
ant and knock it down the side of the pit. These larvae can be easily 
kept in a dish of sand, and their habits watched. 

The most common ant-lion 

in the North is Myrmeleon im- 
maculdtus; the larva of this 
species makes a pitfall. The 
habits of the larvas of Glenurus, 
Dendroleon, and Acanthdclisis, 
three genera that are repre- 
sented in this country, have 
been described by European 
writers. These larvae do not 
dig pitfalls, but partially bury themselves in the sand, from which 
position they throw themselves quickly upon their victims. 




Fig. 345.— Pitfall of an ant-lion. 



NEUROPTERA 



305 



Family ASCALAPHID^ 
The Ascalaphids 

The family Ascalaphidse is quite closely allied to the preceding 
family; but the members of this family can be easily distinguished 
from myrmeleonids by 
the greater length of the 
antennas (Fig. 346) and 
by the fact that in the 
wings there is not an 
elongate cell behind the 
point of fusion of veins 
ScandRi; compare Fig- 
ures 347 and 344. Fig. z^6.— Ululodes hyalina. (From Kellogg, after 
McClendon.) 

The adults are pre- 
dacious; some species fly in the daytime in bright sunshine, but it is 
said that others fly in the twilight. Some species resemble mymieleon- 





I r ca 

Fig. 347. — Wings of Ululodes hyalina. 



ids in appearance, while others resemble dragon-flies. When at rest 
they remain motionless on some small branch or stalk, head down, 
with the wings and antennae closely applied to the branch, and the 
abdomen erected and often bent so as to resemble a short brown twig 
or branch (Fig. 346). 



306 AN INTRODUCTION TO ENTOMOLOGY 

The larvae resemble ant-lions in the form of the body and possess 
the same type of mouth-parts (Fig. 348). They have on each 
segment of the body a pair of lateral finger-like appendages, 
which are clothed with hairs. They do not dig 
pitfalls, but lie in ambush on the surface of the 
ground, with the body more or less covered, and 
wait for small insects to come near them. When 
a larva is full-grown, it spins a spherical silken 
cocoon. An account of the life-history of one 
of our native species, Ululodes hydlina, has been 
published by McClendon ('02). 

The Ascalaphidae of the world have been mon- 
ographed by H. W. Van der Weele ('08). In this 
monograph more than two hundred species are de- 
scribed. The members of this family are chiefly 

p. ^ y ^ tropical insects, but a few species occur in the 

Ululodes hyatina. United States; these represent three genera, which 
(After McClendon.) can be separated by the following table. 

A. Eyes entire Neuroptynx 

AA. Each eye divided into two parts by a groove. 

B. Hind margin of wings entire Ululodes 

BB. Hind margin of wings excised Colobopterus 





Fig. 349. — Wings of Semidalis aleurodiformis. (After Enderlein.) 



NEUROPTERA 



3o; 



Family CONIOPTERYGID^ 

The Mealy-winged Neuroptera 

The Coniopterygidas is a family of limited extent ; and it includes 
only small insects, the smallest of the Nenroptera; the described 
American species measure only 3 mm. or less in length. They are 
characterized by a reduced wing-venation (Fig. 349) and by having 
the body and wings covered by a whitish powder. 

While the adults resemble very slightly other neuropterous insects, 
the larvae resemble those of the Hemerobiidae and allied families in 
form, in the structure of their mouth-parts, in their predacious habits, 
and in their metamorphosis. 

The larvas have been seen to feed upon coccids, aphids, and the 
eggs of the red-spider; they doubtless feed on other small insects. 
When full-grown they make a double cocoon consisting of an outer 
flat layer and an inner spherical case. 

Mr. Nathan Banks ('07) has published a revision of the species 
that have been found in our fauna. This includes eight species, 
representing five genera. 




CHAPTER XII 



ORDER EPHEMERIDA* 

The May-Flies 

The rAembers of this order have delicate membranous wings, which 
arc triangular in outline and are usually furnished with a considerable 
number of intercalary veins and withmany 
cross-veins; the hind wings are much small- 
er than the fore wings and arc sometimes 
wanting. The matt th-parts of the adults are 
vestigial; those of the naiads are fitted for 
chewing. The metamorphosis is incomplete. 

The May -flies or ephemerids are of ten 
very common insects in the vicinity of 
streams, ponds, and lakes; frequently the 
surface of such bodies of water is thickly 
strewn with them. They are attracted by 
lights; and it is not an uncommon occur- 
rence in summertime to see hundreds of 
them flying about a single street-lamp. 

The May-flies are easily distinguished 
from other net-winged insects by the 
shape of the wings and the relative sizes 
of the two pairs (Fig. 350). 

The mouth-parts of the adult are 
vestigial, as these insects eat nothing in 
are very small; they are composed of 




Fig- 350-— A May-fly. 



The antennas 
stout 



this state, 
two short 
segments s u c- 
ceededbya slen- 
der, many-joint- 
ed bristle. The 
thorax is robust, 
with the meso- 
thorax predomi- 
nant; the great 
development of 
this segment is 
correlated with 
the large size of 
the fore wings. 
The abdomen is Fig 
long, soft, and 




composed of ten 



351. — Caudal end of abdomen of Siphlurus alternatus, 
male: g, 10, 11, abdominal segments; c, cerci; mf, median 
caudal filament ; p, penis ;/, forceps-limbs. (After Morgan.) 



*Ephemerida, Ephemera: ephemeron {icp-nM^pov) , 
(308) 



May-fly. 



EPHEMERIDA 



309 



visible segments; the eleventh segment, which bears the cerci, 
is overlapped by the tenth (Fig. 351). The cerci are long, slender, 
and many-jointed; and in some species there is a median caudal 
filament, which resembles the cerci inform; these three organs, 
the two cerci and the median caudal filament, are commonly referred 
to as the caudal setse. In the male there is a pair of clasping 
organs placed ventrally at the extremity of the tenth segment ; these 
are usually two-, three-, or four-jointed and are termed the forceps- 
limbs. Each vas deferens and each oviduct has a separate opening; 
in the male these openings are at the caudal end of the body; in 
the female, between the seventh and eighth stemites. 

In some May-flies the compound eyes are divided; one part of 
each, in such cases, is a day-eye, and the other a night-eye (seepage 
144). 

As the adult May-fly takes no food, its alimentary canal is not 
needed in this stage for purposes of digestion, and, instead of serving 
this function, acts as a balloon, being inflated with air, 
thus lessening the specific gravity of the body and aid- 
ing in flight. 

In this order a marked cephalization of the flight 
function has taken place, which has resulted in a great 
reduction of the hind wings in all Hving forms. In 
some cases (CcBnis et al.), this has gone so far that the 
hind wings are wanting (Fig. 352); but at least one 
pair of wings is present in all members of this order. 

When at rest, the wings are held upright; they are 
never folded over the abdomen. No anal furrow has 
been developed . A striking feature of the wings of May -flies is their 
well-known corrugated or fan -like form, there being a remarkably 




■^^ 




Fig. 353. — Fore wing of Chirotonetes alhomanicatus . 

perfect alternation of so-called convex and concave veins. Correlated 
with the development of the fan-like form of the wings has been the 
development of intercalary veins, that is, veins that did not arise as 
branches of the primitive veins, but were developed in each case as 
a thickened fold, more or less nearly midway between two preexisting 



310 



AN INTRODUCTION TO ENTOMOLOGY 



veins, with which primarily it was connected only by cross-veins. 
The veins labeled IMi, IM3, and ICui in Figures 353 and 354 are 
good illustrations of this type of veins. The initial I in these designa- 
tions is an abbreviation of the word intercalary. Thus the intercalary 
vein between veins Cui and Cu2, i. e., in the area Cui, is designated 
as vein ICui. 

Figures 353 and 354 will aid in the determination of the homol- 
ogies of the wing-veins of May-flies. In these figures convex veins 

are designated by 
plus signs and con- 
cave veins by minus 
signs. In attempt- 
ing to determine 
the homology of a 
vein in a wing 
where the venation 
is reduced, it should 
first be determined 
whether the vein is 
convex or concave, 
as the corrugations 
of the wings of 
May-flies are the 
most persistent fea- 
tures of them. For 
a more detailed ac- 
count of this subject, see Chapter X of "The Wings of Insects." 

The Greek name Ephemeron applied to these insects in the days 
of Aristotle was derived from ephemeras, signifying lasting but a day; 
and from that time to this, frequent references have been made to the 
insects that live only a single day. This brevity of the life of these 
insects is true only of their existence in the adult state. Strictly speak- 
ing, the May-flies are long-lived insects; some species pass through 
their life-cycle in a few weeks in midsummer ; but as a rule one, two, or 
even three years are required for the development of a generation. 
The greater part of this time is passed, however, beneath the surface 
of water, and after the insect emerges into the air and assumes the 
adult form its existence is very brief. With many species the indi- 
viduals leave the water, molt twice, mate, lay their eggs, and die in 
the course of an evening or early morning; and although the adults 
of many genera live several days, the existence of these insects is 
very short compared with that of the adults of other insects. 

The females lay their eggs in water. Some short-Hved species 
discharge the contents of each ovary in a mass. Individuals are often 
found in which there project from the caudal end of the body two 
parallel subcylindrical masses of eggs, one protruding from each of 
the openings of the oviducts. "The less perishable species extrude their 
eggs gradually, part at a time, and deposit them in one or the other 
of the following manners: either the mother alights upon the water 




354. — Hind wing of Chirolonetes alhomanicatiis. 



EPHEMERIDA 



311 



at intervals to wash off the eggs that have issued from the mouths of 
the oviducts during her flight or else she creeps down into the water — 
enclosed within a film of air with her wings collapsed so as to overhe 
the abdomen in the form of an acute narrowly linear bundle, and 
with her setae closed together — to lay her eggs upon the under side of 
the stones, disposing of them in rounded patches, in a single layer 
evenly spread, and in mutual contiguity." (Eaton '83). 




Fig- 355- — Metamorphosis of a May-fly, Ephemera varia: A, adult; B, naiad. 
(After Needham.) 

The metamorphosis of May-flies is incomplete. The wings are 
developed externally, as in the Orthoptera; the development of the 
compound eyes is not retarded; but the immature forms, or naiads, 
are "sidewise developed" to fit them for aquatic life. In most species 
the form of the body of the naiads is elongate and furnished with two 
or three long "caudal set^," that is, cerci and in some a median 
caudal filament; in these respects the naiads resemble, to a greater 
or less degree, the adults (Fig. 355); but except in the early instars 
the abdomen of a naiad is furnished with tracheal gills (Figs. 355 a.nd 
356.) 

The tracheal gills are usually large and prominent; in most 
species there are seven pairs, borne by the first seven 
abdominal segments. They vary greatly in form in the 
different genera. In some each gill is divided into two 
long narrow branches, which lie in one plane (Fig. 355); 
in others the gills consist of a scoop-shaped covering 
piece beneath which is a more delicate part consisting 
of many thread-like branches. A detailed account of 
the various forms of tracheal gills of May -flies is given 
by Miss Morgan ('13). 

The naiads of May -flies are all aquatic; they are 

very active; and are almost entirely herbivorous, -p. ^ 

feeding largely on the decaying stems and leaves of iad of a May- 
aquatic plants, the epidermis of moss and of roots, fly. 




312 



AN INTRODUCTION TO ENTOMOLOGY 



algse, and diatoms. The variations in the details of their habits are 
described as follows by Dr. Needham ('i8). 

"A few, like Hexagenia, Ephemera, and Po/jmz7a/-cv5 are burrowers beneath the 
bottom silt. A few like Canis and Ephemerella, are of sedentary habits and live 
rather inactively on the bottom, and on silt-covered stems. Alany are active 
climbers among green vegetation; such are Callibcetis and Blasturns; and some 
of these can swim and dart about by means of synchronous strokes of tail and gills 
with the swiftness of a minnow. The species of Leptophlebia love the beds of 
i.-jOW-flowing streams, and all the flattened nymphs of the Heptageninse live in 
swiftly moving water, and manifest various degrees of adaptation to withstanding 
the wash of strong currents. The form is depressed, and margins of the head and 
body are thin and flaring, and can be appressed closely to the stones to deflect the 
current." 

There are two features of special interest in the structure of the 
naiads of May -flies: first, the hypopharynx bears a pair of lateral 

lobes, which are believed to be 
: . vestiges of paragnatha ; and sec- 

ond, the presence of accessory 
circulatory organs in the cerci 
and median caudal filament 
'Fig. 3 57)- 

May-fiies exhibit a remark- 
able peculiarity in their develop- 
ment. After the insect leaves the 
water and has apparently as- 
sumed the adult form, that is, 
after the wings have become fully 
expanded, it molts again. These 
are the only insects that molt af- 
ter the}^ have attained functional 
wings. The term 5«6wzag(9 is ap- 
plied to the instar between the 
naiad and the final form of the 
insect, the adult. With some 




Fig. 357. — A, caudal end of abdomen of 
Clo'eon dipterum: h, heart; a, acces- 
sory circulatory organs. B, twer.ty- 
sixth segment of a cercus: 0, orifice in 
blood vessel. (After Zimmerman.) 



species the duration of the sub imago stage is only a few minutes; 
the insect molts on leaving the water; flies a short distance; and 
molts again. In others this stage lasts twenty-four hours or more. 
With many species of May-flies there is great uniformity in the 
date of maturing of the individuals. Thus immense swarms of them 
will leave the water at about the same time, and in the course of a few 
days pass away, this being the only appearance of the species until 
another generation has been developed. The great swarms of "lake- 
flies," Ephemera shnulans, which appear along our northern lakes 
about the third week of July, afford good illustration of this peculi- 
aritv. 

Family EPHEMERID^ 

The May-Flies 

The oraer Ephemerida includes a single family, the Ephemeridas; 
the characteristics of this family, therefore, are those of the order, 
which are given above. 



EPHEMERIDA 313 

Comparatively few writers have made extended studies of the 
classification of the ephemerids ; this is doubtless partly due to the fact 
that pinned specimens usually become shriveled and are very fragile ; 
consequently this order is poorly represented in most collections of 
insects. In spite of this, more than one hundred species have been 
described from the United States. An important paper on the 
classification of May-flies is that by Dr. Needham ('05) in Bulletin 86 
of the New York State Museum. Here are given keys for separating 
the North American genera, one for the adult insects and one for 
the naiads. 






CHAPTER XIII 
ORDER ODONATA=' 



The Dragon-Flies and the Damsel-Flies 

The members of this order have four membranous wings, which are 
finely netted with veins; the hind wings are as large as or larger than 
the fore wings; and each wing has near the middle of the costal margin a 
joint-like structure, the nodus. There are no wingless species. The 
mouth-parts are formed for chewing. The metamorphosis is incomplete. 
Dragon-flies and damsel-flies are very common insects in the 
vicinity of streams, ponds, and lakes; they are well known to all who 
frequent such places. The dragon-flies, especially, attract attention 

on account of their 
largesize(Fig. 358) 
and rapid flight, 
back and forth, 
over the water and 
the shores ; the 
damsel-flies (Fig, 
359) are less likely 
to be noticed, on 
account of their less 
vigorous flight. 

The name of 
this order is evi- 
dently from the 
Greek word odous, 
a tooth; but the 
reason for applying 
it to these insects is 
obscure; it may refer to the tusk-like form of the abdomen. 

In these insects, the head is large; it differs in shape in the two 
suborders as described below. The compound eyes are large; they 
often occupy the greater part of the surface of the head ; in many 
cases the upper facets of the eye are larger than the lower, and in a 
few forms the line of division between the two kinds is sharply 
marked. It is probable that the ommatidia with the larger facets 
are night-eyes, and those with the smaller facets, day-eyes. See 
pages 142 and 1 43 . Three ocelli are present. The antennae are short ; 
they consist of from five to eight segments; of these the two basal 
ones are thick, the others form a bristle-like organ. The mouth- 
parts are well developed; the labrum is prominent; the mandibles 
and maxillas are both strongly toothed; and the labiiun consists of 




Fig. 358. — A dragon-fly, Plathemis lydia. (From San- 
born.) 



"Odonata: odous (65oi5s), a tooth. 



(314) 



ODONA TA 



315 




A damsel-fly. 



three large lobes, which with the labrum nearly enclose the jaws when 
at rest. The thorax is large. The wings are, as a rule, of nearly- 
similar size and structure ; they are richly netted with veins; and the 
costal border of each is divided into basal 
and apical parts by what is termed the nodtis 
(Fig. 364, n). The legs are rarely used for 
walking, but are used chiefly for perching, 
and are set far forward ; the tarsi are three- 
jointed. The abdomen is long, slender, and 
more or less cylindrical; the caudal end is 
furnished with clasping organs in the males. 

A remarkable peculiarity of the order is 
the fact that the copulatory organs of the 
male are distinct from the opening of the 
vasa deferentia; the former are situated on 
the second abdominal segment, the latter on 
the ninth. Before pairing, the male conveys 
the seminal fluid to a bladder-like cavity on 
the second abdominal segment; this is done 
by bending the tip of the abdomen forward. 
Except in the subfamily Gomphinse, the pair- 
ing takes place during flight. The male 
seizes the prothorax or hind part of the head 
of the female with his anal clasping organs; 
the female then curves the end of the abdomen to the organs on the 
second abdominal segment of the male. Pairs of dragon-flies thus 
united and flying over water are a common sight. 

The Odonata are predacious, both in the immature instars and 
as adults. The adults feed on a great variety of insects, which they 
capture by flight; and the larger dragon -flies habitually eat the 
smaller ones, but a large part of their food consists of mosquitoes 
and other small Diptera. 

The eggs are laid in or near water. All of the damsel-flies and 
many dragon-flies are provided with an ovipositor, by means of 
which punctures are made in the stems of aquatic plants, in logs, in 
wet mud, etc., for the reception of the eggs. The females of those 
dragon-flies that lack a well-developed ovipositor deposit their eggs 
in various ways. In some species the female flies back and forth 
over the surface of the water, sweeping down at interv-als to touch it 
with the tip of her abdomen and thus wash off one or more eggs into 
it. In other species the eggs are laid in a mass on some object just 
below the surface of the water; some species do this by alighting 
upon a water-plant, and, pushing the end of the abdomen below the 
surface of the water, glue a bunch of eggs to the submerged stem or 
leaf; in other species the mass of eggs is built up gradually; the 
female will poise in the air a short distance above the point where the 
mass of eggs is being laid, and at frequent intervals descend with a 
swift curved motion and add to the egg-mass and then return to her 
former position to repeat the operation. Still other species hang their 



.IG 



AN INTRODUCTION TO ENTOMOLOGY 




eggs in long gelatinous strings, on some plant stem at the surface of 
the water. 

The metamorphosis is incomplete. The naiads are all aquatic 
except those of a few Hawaiian damsel-flies, which live on moist soil 
under the leaves of liliaceous plants. The wings 
are developed externally, and the development of 
the compound eyes is not retarded, as it is with 
larvas. The adaptations for aquatic life differ in 
the two suborders and are described later. 

All naiads of the Odonata are predacious. 
The mouth is furnished with well-developed 
mandibles and maxillae, all of which are armed 
with strong teeth. But none of these is visible 
when the insect is at rest. The lower lip is greatly 
enlarged, and so formed that it closes over the 
jaws, conceahng them. For this reason it has been 
termed the mask. But it is much more than a 
mask; it is a powerful weapon of oft'ence. It is 
greatly elongated and is jointed in such a way that 
it can be thrust out forward in front of the head. 
It is armed at its extremity with sharp hooks, 
for seizing and retaining its prey (Fig. 360). 

The order Odonata is divided into three sub- 
orders. One of these suborders, the Anisozygop- 
Under side tera, is composed almost entirely of fossil forms, 
of head of a naiad being represented among living insects by a single 
of adamseU^with genus, Epiophlebia, which is found in Japan. The 
(Afte™Sharp.*) ^ ' other two suborders are well represented in this 
country ; one of them consists of the dragon-flies, 
the other of the damsel-flies. 

Suborder ANISOPTERA* 

The Dragon-Flies 

The dragon-flies 
are easily recognized 
by the relative size of 
the two pairs of wings, 
and by the attitude of 
the wings when at 
rest (Fig. 361). The 
hind wings are larger 
than the fore wings 
and are of a somewhat 
dift'erent shape; but 
the most striking 
characteristic is the 
fact that the wings 
are extended horizontally when at rest. 



4 

Fig. 360, 




Fig. 361. — A dragon-fly, Libellula luduosa. 



"Anisoptera : anisos (Hvktos), unequal; pteron {wTep6v), a wing. 



ODONATA 317 



The head is large, broad, often semi-globose, and concave behind. 
The wings are very strong. An important factor in the strengthening 




Fig. 362. — -Wings of naiads of Gomphus descriptus, early stages. (From Comstock 
and Needham.) 

of the wings of these insects is the development of a series of cor- 
rugations, which has resulted in certain veins becoming convex and 
others concave; this has progressed so far that there is a very perfect 
alternation of convex and concave veins. 

The habits of dragon -flies have been carefully studied by Professor 
Needham ('18), who writes as follows: 

"Among the dragon-flies are many superb flyers. The speed on the wing of 
Trdmea and Anax equals, and their agility exceeds, that of swallows. They all 
capture their prey in flight; and are dependent on their wings for getting a living. 
But the habit of flight is very different in different groups. Only a few of the 




Fig. 363. — Tracheation of the wings of a grown naiad of Gomphus descriptus. 
(After Needham.) 



318 



AN INTRODUCTION TO ENTOMOLOGY 



strongest forms roam the upper air at will. There is a host of beautiful species, the 
skimmers or Libellulidce, that hover over ponds in horizontal flight, the larger 
species on tireless wings, keeping to the higher levels. The stronger flying ^schni- 
dae course along streams on more or less regular beats; but the Gomphines are 
less constantly on the wing, flying usually in short sallies, from one resting place 
to another, and alighting oftener on stones or other flat surfaces than on vertical 
stems." 

The characters presented by the venation of the wings of the 
Odonata are much used in the classification of these insects. In 
general the veins and areas of the wings are designated as in the 
accounts of the wings of other orders of insects ; but there are certain 
features in the wings of these insects that are peculiar to them. 

The most distinctive feature of the wings of the Odonata is the 
fact that in the course of their development one or more branches, 
usually two, of the medial trachea invade the area of the radial sector. 




Fig. 364. — Wings of Gomphus descriptus. In the front wing, cells or areas are 
labeled; in the hind wing, veins. 

This results in vein Rg occupying a position behind one or more, 
usually two, of the branches of media. Figure 362 represents the 
tracheation of the wings of two naiads of Gomphus descriptus; the 
wing shown at A is of a very young naiad ; that at B is of a somewhat 
older one. In the wing shown at A, the branches of trachea M are in 
their typical position; in the wing shown at B, trachea Mi is in front 
of trachea Rs. Figure 363 represents the tracheation of a full-grown 
naiad of the same species. In this stage of the development of the 
wings, both tracheas Mi and Mo are in front of trachea Rs; and it is 
in this position that the veins of the adult wing are developed (Fig. 
364)- 



ODONA TA 



319 



By comparing the figure of the wing of an adult (Fig. 364) with 
that of the full-grown naiad (Fig. 363), it will be seen that the 
chlique vein marked o is not a cross-vein but a section of vein R?; 
so too, what appears to be another cross-vein, labeled 5 «, is also a 
section of vein Rg; this section of vein Rs is known as the subnodus. 
It will also be seen that what appears to be the base of the radial 
sector, labeled b r, isa secondarily developed vein which connects the 
radial sector with a branch of media ; this secondary vein is known 
as the bridge. The beginning of the formation of the bridge is shown 
in Figure 363.* 

The more important of the other special terms used in descriptions 
of the wings of dragon-flies are the following : Much use is made in 
taxonomic work of the two series of cross-veins that are nearest the 
costal margin of the wing ; those of these cross-veins that are situated 
between the base of the wing and the nodus are termed the antenodal 
cross-veins; the first of these two series of antenodal cross-veins ex- 
tend from the costa to the subcosta; the second from the subcosta 
to the radius; the antenodal cross-veins are termed the antecubital 
cross-veins b}^ some writers. The two series of cross- veins nearest to 
the costal margin of the wing and between the nodus and the apex 
of the wing are termed 
the postnodal cross- 
veins; the first of the 
two series of postnodal 
cross-veins extend 
from the costa to vein 
R] ; the second, from , 
vein Ri to vein Mr, 
the postnodal cross- 
veins are teimed the 
postciibital cross-veins 
by some writers. Near 
tlie base of the wing 
there is in dragon-flies 
a well-marked area of 
the wing, which is usu- 
ally triangular in out- 
line (Fig. 364, t); this. 

is the triangle; fre- . ■ ^ t a 

,1 ,1 , ^. 1 . of a naiad of a drag- 
quently the triangle is ^j^.f iy_ Tetrago- 
divided by one or neuHa. 
Fig.365.-Hind-intestineand part more cross-veins into 
of the tracheal system of a naiad two or more cells. The area lying imme- 
ot /EscJmacyanea: R, R, R, R,vec- diatelv in f ront of the triangle (Fig. 364, 
rif,;.T„\vS^tctaUubS! f.'' terrnedthe ™f.rt™„gfe; like the 
M, Malpighian tubes. (From triangle this area may consist of a single 
Sharp, after Oustalet.) cell or may be divided by one or more 





Fig. 366. — • Exuviae 



*The conclusions regarding the homologies of the wing-veins given here are 
based on investigations by Dr. Needham the results of which were published by 



320 AN INTRODUCTION TO ENTOMOLOGY 

cross-veins. Other named areas are thebasal anal area (Fig. 364, ha) 
and the cubital area (Fig. 364, ca). 

The writer has given in his "The Wings of Insects" an extended 
discussion of the wings of Odonata, illustrated by many figures, in- 
cluding a plate in which adjacent veins are represented in different 
colors, so that the course of each can be easily followed. 

With the naiads of dragon-fiies there is a remarkable modification 
of the organs of respiration, which fits these insects for aquatic life. 
The caudal part of the alimentary canal, the rectum, is modified so 
as to constitute a tracheal gill. It is somewhat enlarged ; and its walls 
are abundantly supplied with tracheae and tracheoles (Fig. 365). 
Water is alternately taken in and forced out through the anal opening; 
by this process the air in the tracheae, with which the walls of the 
rectum are supplied, is purified in the same manner as in an ordinary 
tracheal gill. 

The rectal tracheal gill of the naiads of dragon-flies is an organ of 
locomotion, as well as of respiration. By drawing water into the rec- 
tiun gradually, and expelling it forcibly, the insect is able to dart 
through the water with considerable rapidity. This can be easily 
observed when naiads are kept in an aquarium. 

When the naiad of a dragon-fly is fully grown it leaves the water 
to transform. The skin of the naiad splits open on the back of the 
thorax and head, and the adult emerges, leaving the empty skin of 
the naiad clinging to the object upon which the transformation 
took place. Figure 366 represents such a skin clinging to the stem 
of a water plant. 

The suborder Anisoptera includes two families, the ^Eschnidag 
and the Libellulidae ; each of these families is represented in our 
fauna by many genera and species. These are enumerated in the 
"Catalogue of the Odonata of North America" by Muttkowski ('10). 
The two families can be separated by the characters given below. 

Family ^SCHNID^ 

The Mschnids 

In this family the triangle (Fig. 364, t) is about equally distant 
from the arculus (Fig. 364, ar) in the fore and hind wings; and, 
except in the genus Cordulegdster, there is an oblique brace-vein 
extending back from the inner end of the stigma (Fig. 364). 

The aeschnids are mostly large species ; among them are the largest, 
fleetest, and most voracious of our dragon-flies. Some of them roam 
far from water and are commonly seen coursing over lawns in the 
evening twilight; but most of them fly over clear water. 



Comstock and Needham ('gS-'gg) and by Needham ('03). These conclusions 
have been questioned by Tillyard ('22) and by Schmieder ('22); but I do not feel 
that it would be wise to modify them before a much more extended investigation 
of the subject has been made. 



ODONA TA 



321 



Family LIBELLULID^ 

The Ltbellulids or Skimmers 

In this family the triangle in the hind wing is much nearer the 
arculus than is the triangle of the fore wing ; and there is no oblique 
brace-vein extending back from the inner end of the stigma, as in 
the ceschnids. 

This is a large family including many of our commonest and 
best-known species of dragon-flies; many of them are familiar figures 
flying over ponds and ditches and by roadsides. Most of them are 
of well-sustained flight, and are seen continually hovering over the 
surface of still water; this suggested the common name skimmers 
which has been applied to them. 




Fig- 367. — A damsel-fly. 



Suborder ZYGOPTERA* 
The Damsel-Flies 

The damsel-flies differ from the 
dragon-flies in that the two pairs 
of wing:s are similar in form and 
are either folded parallel with the 
abdomen when at rest (Fig. 367) 
or uptilted (Testes). The head is 
transverse, each eye being borne 
by a lateral prolongation of the 
head. The females possess an 
ovipositor by means of which the 
eggs are placed in the stems of 
aquatic plants, sometimes beneath 
the surface of the water. 

The name of the suborder 
probably refers to the fact that 
the wings are brought together 
when at rest. 




Fig. 368. — Wing of Lestes rectangularis : 0, oblique vein; br, the bridge. 



''Zygoptera: zygon (,^vy6v), yoke; pteron {irrepdv), a wing. 



322 



AN INTRODUCTION TO ENTOMOLOGY 



Unlike the dragon-flies, the damsel-flies are comparatively feeble 
in their flight. They are found near the margins of streams and 
ponds, in which the immature stages are passed. 

Most of the features in the venation of the wings of dragon-fliti 
described on earlier pages are also characteristic of the wings of damse'i- 
flies. Figure 368 represents an entire wing of Lestes rectangularis; 




Fig. 369. — Base of fore wing of Lestes rectangularis: br, the bridge; q, quadrangle; 
sq, subquadrangle. 

in this figure o indicates the oblique vein, and hr the bridge. In 
Figure 369 the base of this wing is represented more enlarged, and 
the principal veins are lettered. 

In the suborder Zygoptera the cubitus and the first branch, vein 
Cui, extend in a comparatively direct course from the base of the 
wing outward (Fig. 369); the abrupt bends in these veins in the 
region of the triangle, which are so characteristic of the Anisop- 
tera, are only slightly developed here. This results in the areas 
corresponding to the triangle and the supertriangle of the Anisop- 
tera being in direct line and forming an area which is often 
quadrangular; this area is termed the quadrangle (Fig. 369, q). In a 

large part of this or- 
der the cross-vein sep^ 
arating the parts of 
the quadrangle corre- 
spond ingto th e triangle 
and the supertriangle 
of the Anisoptera is 
lacking, in which case 
the quadrangle con- 
sists of a single cell 
Fig. 370.— Base of wing of Heliocharis. ^~*~-^ (Fig. 369, g). In SOme 

members of this sub- 
order it is present; in Figure 370, representing the base of a wing 
of Heliocharis, the two cells of the quadrangle are labeled t and .j to 




ODONA TA 



323 



facilitate comparison with figures of wings of Anisoptera. In certain 
other members of this subor- 
der the quadrangle is divided 
into several cells by cross- veins 
(Fig. 37i). 

The cubital area of the 
wing is usually quadrangular 
in outline in the Zygoptera, 
and is termed the subquad- 
rangle (Fig. 369, sq). Like 
the quadrangle, it may con- 
sist of a single cell or it may 
be divided by cross-veins (Fig. 
371)- 

The naiads of damsel-flies have three plate-like tracheal gills at 
the caudal end of the body (Fig. 372). The structure of these gills 
is illustrated by Figure 373 ; at A is represented an entire gillshowing 
the trachea; and at B, part of a gill more magnified, showing both 
tracheae (T) and tracheoles (t). 




Fig. 371. 



of wing of He.'cprina. 





Fig. 373. — Tracheal gill of a damsel-fly: 

A, entire gill showing the tracheae; 

B, part of gill more magnified , show- 
ing both tracheae (T) and tracheoles 
(t). 



Fig. 372. — Naiad of a 
damsel-fly, Argia. 



The suborder Zygoptera includes two families, the Agrionidee 
and the Coenagrionidas. The genera and species of these families are 
enumerated by Muttkowski ('10). The two families can be separated 
as follows. 

A. Wings with many, at least five, antenodal cross-veins Agrionid.-e 

AA. Wings usually with only two antenodal cross- veins, rarely with three or 
four CCENAGRIONID/E 



324 AN INTRODUCTION TO ENTOMOLOGY 

Family AGRIONID^ 

The True Agrionids 

In the Agrionidse the wings are furnished with many antenodal 
cross-veins; and, although the wings are narrow at the base, they 
are not so distinctly petiolate as in the next family. These insects 
may be termed the true agrionids, as owing to a misapplication of the 
generic name Agrioti the members of the next family have been 
incorrectly known as the agrionids. 

Here belong the most beautiful of our damsel-flies, whose metallic 
blue or green colors are sure to attract attention. They are feeble in 
flight and do not go far from the banks of the pond or stream in 
which they were developed. 

There are only two genera of this family in our fauna. These are 
Agrion, which has been commonly known as Calopteryx, and Hetce- 
rina. In Agrion the wings are broad and spoon-shaped. In HetcB- 
nna the wings are rather narrow, and in the males the base of one or 
both pairs is red. 

Family CCENAGRIONID^ 

The Stalked-winged Damsel-Flies 

The members of this famiily are easily recognized by the shape 
of their wings, which are long, narrow, and very distinctly petiolate 
(Fig. 368); and by the fact that in each wing there are only two 
antenodal cross-veins, except in a few cases where there are three or 
four. 

To this family belong the smallest of our damsel-flies; but while 
our species are of small or moderate size, there exist in the tropics 
species that are the largest of the Odonata. Some of our species are 
dull in color; but many are brilliant, being colored with green, blue, 
or yellow. This family includes the greater number of our damsel-flies. 



CHAPTER XIV 
ORDER PLECOPTERA* 

The Stone-Flies 

The members of this order have four membranous wings. In some 
genera the branches of the principal veins are reduced in number and 
there are comparatively few cross-veins; in others, accessory veins are 
developed and there are many cross-veins; in most genera the hind wings 
are much larger than the fore wings, and are folded in plaits and lie 
upon the abdomen when at rest. The mouth-parts are of the chewing 
type of structure, but are frequently vestigial in the adidt. The cerci are 
usually long and many-jointed. The metamorphosis is incomplete. 

Members of this order are common insects in the vicinity of rapid 
streams and on wave-washed rocky shores of lakes ; but they attract 
Httle attention on account of their inconspicuous colors and secretive 
habits. They are called stone-flies because the immature forms are 
very abundant under stones in the beds of streams. 

In the adults the body is depressed, elongate, and with the sides 
nearly parallel (Fig. 374). 
The prothorax is large. The 
antenna are long, tapering, 
and many-jointed. The 
mouth-parts are usually 
greatly reduced. In some 
genera the mandibles are al- 
most membranous, but in 
others they are firm and 
toothed, being well fitted 
for biting. The maxillae 
exhibit variations in the 
degree of their reduction 
similar to those shown by 
the mandibles. The maxil- 
lary palpi are five-jointed. 
The labial palpi are three- 
jointed. The legs are widely 
separated, except the fore 
legs in the Pteronarcidse; 

the tarsi are three-jointed. The hind wings are a little shorter than 
the fore wings, but usually, owing to the expansion of the anal area, 
they are considerably larger than the fore wings ; in a f ev\^ genera the 
hind wings are smaller than the fore wings ; in some species the wings 
of the male are greatly reduced in size, and in others the males are 
wingless. When at rest, the wings are folded in plaits and lie upon the 

*Plecoptera: pieces (wXiKo^), plaited; pteron (irTepdv), a win^. 

Cb25) 




A stone-fly, Pteronarcys dorsata. 



326 AN INTRODUCTION TO ENTOMOLOGY 

abdomen, as shown on the left side of Figure 374. The cerci are u'^u- 
ally long and many -jointed; but they are rudimentary in the 
Nemouridas. 

The stone-flies are unattractive in appearance ; in most of them 
the colors are obscure, being predominantly black, brown, or gray ; but 
some of them that are active in the da}i;ime and inhabit foliage are 
green. Their powers of flight are quite limited; they are usually 
found crawling about on stones or on plants near streams. Several 
of the smaller species appear in the adult state upon snow on warm 
days in the latter half of winter. They become more numerous in 
early spring and often find their way into our houses. The most 
common one of these in central New York is the small snow-fly, 
Cdpnia pygmcea. 

It is probable that most adult stone-flies eat nothing; this can 
be inferred from the reduced condition of their mouth-parts. But it 
has been shown by Newcomer ('18) that several species of Tmiiopteryx, 
which are equipped with well-developed mouth-parts, feed upon the 
buds and leaves of plants. One species in particular, T. pactfica, is a 
serious pest in the Wenatchee Valley, Wash., where it bites into the 
buds of fruit trees. 

One of the more striking features of the venation of the wings of the Plecoptera 
is a lack of uniformity in the number and courses of the subordinate veins. Not 
only are striking differences in wing-venation to be observed between different 
individuals of the same species, but frequently the wings of the two sides of an 
individual will vary greatly in venation. This is especially true as to the number 
of cross-veins and the branching of the veins in the distal parts of the wings. 
On the other hand, the characters presented by the trunks of the principal veins 
are quite constant. 

There is one characteristic of the wings of the Plecoptera that is so constant 
that it may be considered an ordinal character. This is the fact that in the wings 
of the adult the radial sector of the hind wings is attached to media instead of to 
radius (Fig. 3766). This switching of the radial sector of the hind wings is true 
only of the venation of the adult. In the wings of naiads the trachea Rs is a 
branch of trachea R. 

There are certain features of the wings of Plecoptera, which, although not 
always constant, occur in so large a portion of the members of the order that they 
may be considered characteristic; these are the following, all of which are repre- 
sented in Figure 3766; The presence of the radial cross-vein {r). The absence of 
cross- veins in cell R and in the basal part of area Ri. (Cross- veins are found in 
cell R in Pteronarcys.) The strengthening in the fore wings of the area between 
media and vein Cui and of that between veins Cuj and Cuj by the development 
of many cross- veins. The reduction of media to a two-branched condition. The 
reduction of the radial sector to a two-branched condition. (This reduction of the 
i-adial sector is apparent only after an extended study of the wings of stone-flies. 
In many cases, of which the form represented by Figure 3766 is one, accessory 
veins have been developed on vein R2 +3 which appear to be the primitive branches 
of the radial sector; but these accessory veins are very inconstant in number and 
position.) And the unbranched condition of the first anal vein. 

In concluding this brief summary of the special features of the wings of the 
Plecoptera it seems desirable to define some terms frequently used by writers on 
this order. 

The transverse cord. — In many genera of this order there is a nearly continuous 
series of cross-veins extending across each wing just beyond the middle of its 
length; this series of cross- veins is termed the anastomosis by many writers On 
the Plecoptera. As it is not formed by an anastomosing of veins, the use of the 
term transverse cord is preferable. 



PLECOPTERA 



327 



The pterosligma. — In most members of this order a specialized pterostigma has 
not been developed; but the term pterostigma is commonly applied to the cell 
beyond the end of the subcosta and between the costa and vein Ri, even though 
it is of the same color and texture as the remainder of the wing. 

The basal anal cell. — A very constant feature of the anal area of the wings of 
Plecoptera is the presence of a cross- vein near the base of the wing, which extends 
from the first anal vein to the second. The cell that is closed by this cross- vein is 
termed the basal anal cell (Fig. 376^, ba). 

The females drop their eggs in a mass in water. I have taken 
females of Perla and of Pteronarcys at lights, each with a mass of 
eggs hanging from the abdomen. 

The metamorphosis is incomplete. The immature forms are all 
aquatic. These naiads are common on the lower surface of stones in 
rapids. They can be found easily by lifting stones from such situations 
and turning them over quickly, when the na- 
iads will be found clinging to the stones 
with their fiat bodies closely appressed to 
them and their legs, antenna, and cerci ra- 
diating on the surface of the stone , but they 
are apt to run away quickly. 

The naiads of stone-flies live only in 
well-aerated water; they are not found in 
stagnant water or in foul streams. They are 
said to feed on other aquatic insects, includ- 
ing smaller individuals of their own species; 
but according to the observations of Dr. 
P. W. Claassen they are largely vegetable 
feeders. 

The body is depressed (Fig. 375); the 
antenna are long, so too are the cerci Most 
species possess tracheal gills, situated usually 
on the ventral side of the thorax just be- 
hind the base of each leg ; but tracheal gills 
are found in some species either on the un- 
der side of the head, on the basal abdom- 
inal segments, or at the tip of the abdo- 
men. A large nimiber of the smaller species are destitute of 
tracheal gills; in these the air supply is absorbed through the thin 
cuticula of the ventral surface. The colors of naiads are often brighter 
than those of adults. 

When full-grown the naiads leave the water and transform on some 
near-by object. The empty exuviae are often found clinging to stones 
or logs projecting from water or on the banks of streams. 

According to a recent classification of this order, that of Tillyard 
('21), it includes seven families; but only four of these families are 
represented in our fauna. A monograph of the North American 
species of the order is in preparation by Professor J. G. Needham 
and Professor P. W. Claassen; this is nearly completed and probably 
will be published soon. The four families of our fauna can be separat- 
ed by the following table. 




Fig. 375. — Naiad of a 
stone-fly, Acroneura. 



328 



AN INTRODUCTION TO ENTOMOLOGY 



A. Anal area of the fore wings with two or more series of cross-veins (Fig. 

376a). p. 328 PTERONARCID.E 

AA. Anal area of the fore wings with not more than a single series of cross- veins, 
usually with no cross-veins beyond the basal anal cell. 
B . Media of the fore wings separating from radius gradually, the two forming 

a sharp angle (Fig. 3766). p. 328 Perlid^ 

BB, Media of the fore wings separating from radius abruptly, the two form- 
ing a blunt angle (Fig. 376c), 
C. Anal area of the fore wings with a forked vein arising from the basal 
anal cell (Fig. 376a). Cerci vestigial, p. 330. Nemourid^ 

CC. Anal area of the fore wings with only simple veins arising from the 

basal anal cell (Fig. 376c?). Cerci well developed, p. 330 

Capniid^ 

Family PTERONARCID^ 

This is a small family which is represented in North America by 
only two genera and by but few species. 

Pterondrcys. — This genus includes the largest of our stone-flies. 
Figure 374 represents a common species. The venation of the wings 



^Tm Sr, 







Fig. 376a. — Wings of Pteronarcella badia. 

is reticulate ; the reticulation is irregular and extends in the fore vnngs 
from the costa through the anal area. 

A remarkable feature of members of this genus is that vestiges of 
tracheal gills are retained by the adults. 

Pteronarcella. — This genus includes smaller species than the pre- 
ceding one, and the venation of the wings is more regular than in 
Pteronarcys (Fig. 376a). 

Family PERLID^ 



The members of this family differ from the Pteronarcidae in the 
smaller niunber of cross- veins in the anal area of the fore wings. 



PLECOPTERA 



329 



there being usually no cross-veins beyond the basal anal cells (Fig. 
3766); and they differ from the following families in that media of 




, 2dA 

Fig. 376^. — Wings of Isogenus sp. 




2^^ 
Fig. 376c. — Wings of Nemoura sp. 



330 



^A^ INTRODUCTION TO ENTOMOLOGY 



the fore wings separates from radius gradually, the two forming a 
sharp angle (Fig. 37 6b). 

This is the largest of the families, including a large portion of the 
genera and species found in our fauna; fourteen genera have been 
described from this region. 

Family NEMOURID^ 

In this and the following family the media of the fore wings 
separates from radius abruptly, the two forming a blunt angle (Fig. 
376c). In this family the second and third anal veins of the fore 
wings coalesce for some distance beyond the basal anal cell, forming a 
forked vein (Fig. 376c), and the cerci are vestigial. 

The family is represented in our fauna by nine genera. Our more 
common representatives are small, dusky, and grayish species that 
are found emerging throughout the spring of the year. 

Family CAPNIID^ 

In this family, as in the Nemouridae, the media of the fore wings 
separates from radius abruptly, the two forming a blunb angle (Fig. 
3,7 6d); but in this family there are in the anal area of the fore wings 




^•4+5 



Fig. 376^. — Wing of Capnia sp. 

only simple veins arising from the basal anal cell (Fig. 376(f), and the 
cerci are well developed. This is a small family which is represented 
in our fauna by only three genera. 

The members of this family that are most often seen are the little 
black species of Capnia that appear on snow on warm days in the 
latter half of winter and in early spring. The naiads of these live chiefly 
in small brooks. 



CHAPTER XV 
OPJ)ER CORRODENTIA* 

The Psocids and the Book-Lice 




Fig- 377- — A winged psocid, 
Cerastipsocus venosus. 



The winged members of this order have Jour membranous wings, 
wiTn the veins prominent, but, with comparatively Jew cross-veins; the 
Jore wings are larger than the hind wings; 
and both pairs when not in use are placed 
rooj-like over the body, being almost vertical, 
and not Jolded in plaits. The mouth-parts 
are formed Jor chewing. The metamorphosis 
is gradual. 

The best-known representatives of this 
order are the minute, soft-bodied insects 
which are common in old papers, books, 
and neglected collections and which have 
received the popular name book-lice. 
These low, wingless creatures form, how- 
ever, but a small part of the order. The more typical winged forms 
(Fig. 377) bear a strong resemblance to plant-lice or aphids. The body- 
is oval, the head free, and the protho- 
rax small. The fore wings are larger 
than the hind wings; and both 
pairs when not in use are placed roof- 
like over the body, being almost 
vertical, and not folded in plaits. 
The wing-veins are prominent, but 
the venation of the wings is reduced. 
The tarsi are two- or three-jointed. 
Cerci are wanting. 

The mouth-parts are of especial 
interest on account of the presence 
of well-preserved paragnatha. Fig- 
ure 378 represents the mouth-parts 
of the common book-louse, Troctes 
divinatorius , as figured by Snodgrass 
('05). The mandibles 0) are of the 
ordinary, strong, heavy, biting type. 
The maxillag (m) consist each of a 
body piece, a weakly chitinized terminal lobe, and a four-jointed 
palpus. The paragnathus if, J) is represented in the figure at A, 
with the maxilla; it lies above the maxilla and is, therefore, in its 
typical position between the maxilla and the mandible of the same 

*Corrodentia: Latin corrodens, gnawing. 
r331) 




Fig. 378. — Mouth-parts of a book- 
louse, Troctes divinatorius: A , max- 
illa and paragnathus of right side, 
ventral view; w, maxilla; /, /, 
paragnathus; p, protractor mus- 
cle; r, retractor muscle. .B, man- 
dibles. C, labium, ventral view; 
p, palpus. (After Snodgrass.) 



332 



AN INTRODUCTION TO ENTOMOLOGY 



side. Note that the figure is a ventral view, hence the paragnathus 
is represented as passing beneath the maxilla. The paragnatha have 




Fig. 379. — The wings of a psocid. 

been known as the fur ecu maxillares. The labium (C) bears a pair of 
one-jointed palpi. 

The venation of the wings is distinctively characteristic in this order. 
The venation is more or less reduced; but its most characteristic 
feature is the bracing of the wing by anastom.oses of the principal 




Fore v.'ing of a full-grown nymph of a psocid. 



veins instead of by cross-veins. This is well shown by the wings of 
Psocus (Fig. 379). The determination of the homologies of the 
wing-veins in this insect was accomplished by a study of the trachea- 
tion of the wings of nymphs. Figure 3 So represents the tracheation 
of a fore wing of a full-grown nymph of Psocus. 

There are no cross-veins in the wings of Psocus; the arculus (ar) 
in the fore wing is merely the base of media, and what appear as 



CORRODENTIA 333 

cross-veins in the central portion of the wing are sections of rr.edia 
and cubitus. In some genera, however, the radial cross-vein is present, 
and in some, instead of an anastomosis of veins M and Cui, these 
veins are connected by a medio-cubital cross- vein. 

The metamorphosis is gradual. The nymphs resemble the adults 
in the form of the body, but lack wings and ocelli in those species 
that are winged in the adult; in the wingless species the differences 
between the young and the adult are even less marked. 

The Corrodentia of the United vStates and Canada represent tvvo 
families, which can be separated as follows. 

A. Wings well developed ; ocelli present Psocid^ 

AA. Wings absent or vestigial; ocelli absent Atropid^ 

Family PSOCID^E 
The P sec ids 

The family Psocidae includes the more typical members of the 
Corrodentia, those in which the wings are well developed (Fig. 377). 
Usually the wings extend much be>'ond the end of th.e abdomen; but 
short -winged forms occur in species which ordinarib/ are long-winged. 
Of course the young of all are wingless, and there is a gradual develop- 
ment as the insect matures. The antennge consist of onlv' thirteen 
segments; this will enable one to separate the immature forms from 
the Atropids, in which the antennas have a greater number of segments. 

The psocids occur upon the trunks and leaves of trees, and on 
stones, walls, and fences. They feed upon lichens, fungi, and probabl ;^ 
other dry vegetable matter. They are sometimes gregarious. I have 
often seen communities of a hundred or more closely huddled together 
on the trunks of trees, feeding on lichens. 

The eggs are laid in heaps on leaves, branches, and the bark of 
trunks of trees. The female covers them with a tissue of threads. 
It is believed that both sexes have the power of spinning threads. 
The silk is spun from the labium. 

More than seventy species, representing eleven genera, have been 
described from our fauna. 



Family ATROPID^ 
The Book-Lice and Their Allies 

The family Atropidse includes small Corrodentia, which are 
wingless or possess only vestigial wings. The most commonly ob- 
served species are those known as book-lice, which are the minute 
soft-bodied insects often found in old books (Fig. 381). Of these the 
two following species are the best known. 

Troctes divinatorius. — This is a wingless species which measuies 
about I mm. in length; it is grayish white, with black eyes. 



334 



AN INTRODUCTION TO ENTOMOLOGY 



Atropos pulsatoria. — In this species the fore wings are represented 
by small convex scales ; it is of a pale yellowish white color and is a 
little more than i mm. in length. 

Each of these species has been known as the death-watch, as they 
have been believed by superstitious people to make a 
ticking sound that presaged the death of some person 
in the house where it is heard. It is not probable that 
such minute and soft insects can produce sounds 
audible to human ears. The sounds heard were prob- 
ably made by some wood-boring beetles, Anohiidce, 
which are also known as the death-watch. 

Book-lice are found chiefly in damp, well-shaded 
rooms, not in general use. They do not attack man, 
but feed upon dead vegetable and animal matter, as 
the paste in book-bindings, wall-paper, and photo- 
graphs. They rarely occur in sufficient numbers to 
do serious injury. They can be destroyed by fumigating the infected 
room with hydrocyanic acid gas. This, however, should be used only 
by experienced persons. Ordinarily a prolonged heating and drying 
of the roam will be sufficient to destrov them. 




Fig. 381.— A 
book-louse. 



CHAPTER XVI 
ORDER MALLOPHAGA* 

The Bird-Lice 

The members of this order are wingless parasitic insects with chewing 
mouth-parts. Their development is without metamorphosis. 

The bird-lice resemble the true lice in form, being wingless, and 
having the body more or less flattened; certain species that infest 
domestic fowls are well-known examples. These insects differ from 
the true hce in having chewing mouth-parts. They feed upon feath- 
ers, hair, and dermal scales, while the true lice, which constitute the 
order Anoplura, have sucking mouth- parts, feed upon blood, and 
infest only mammals. 

The Mallophaga infest chiefly birds, and on this account 
the term bird-lice is applied to the entire group; a few genera, 
however, are parasitic upon mammals. Some writers term the Mallo- 
phaga the biting lice, which is a more accurate designation; but the 
name bird-lice is more generally used. 

The bird-lice are small insects. The more common species range 
from I mm. to 5 mm. in length. The mouth-parts are on the under 
side of the head, the most anterior part of the head being a greatly 
enlarged clypeus ; they are of the mandibulate type; and paragnatha 
("furcce maxillares") have been found in several species (Snod- 
grass '05). There is a pair of "simple eyes" located in the lateral 
margins of the head. The structure of these eyes has not been de- 
scribed; but judging from their position they are probably degenerate 
ommatidia and not oceUi. The front legs are shorter than the others 
and are used to convey food to the mouth. 

There is an interesting correlation between the habits of these 
insects and the structure of their feet. The tarsi of those species 
that feed on mammals are one-clawed and fitted for folding against 
the tibiffi; they are organs well adapted for clinging to hairs. Those 
species that feed on birds have two-clawed tarsi and are better fitted 
for running. The above distinction is not quite accurate, as a few 
two-clawed species feed on kangaroos, wallabies, and wombats. 



*Mall6phaga: mallos {na\\6s), wool; phagein {(payeip), to eat. 
(335) 



-336 • AN INTRODUCTION TO ENTOMOLOGY 

The accompanying figures represent some of our common species. 




Fig. 2)^2.—Goniodes stylif- 
er. (From Law.) 



Fig- 383. — Tricho- 
d e c t e s I at u s. 

(From Law.) 



Fig 384 — 
Trichodectes 
spheroceph- 
aliis. (From 

Law.) 




Fig. 2,^^. — Tri- 
chodectes sca- 
Hris. (From 

Law.) 




Fig 386 —Tncho 
dectes equt. 
(From Law.) 



Gcniodes stylifer (Fig. 382) infests turkeys; Trichodectes Idtus (Fig. 
383), dogs; Trichodectes spherocephalus (Fig. 384), 
sheep; Trichodectes scaldris (Fig. 385), domestic cat- 
tle; and Trichodectes equi (Fig. 386), horses and asses. 
The eggs of the Mallophaga are glued to the 
hairs or feathers of their hosts. The development 
takes place on the body of the host and is without 
metamorphosis. The young are not so dark in color 
as the adults and the cuticula is less densely chitin- 
ized. The ametabolous condition of these insects is 
believed to be an acquired one, a result of their 
parasitic habits. 

The bird-lice are well known to most people who 
have pet birds or who keep poultry. It is to free 
themselves from these pests that birds wallow in 
dust. When poultry are kept in closed houses they should be provided 
with a dust-bath. AH poultry houses should be cleaned at least twice 
a year, and the old straw burned. Sprinkling powdered sulphur in 
the nests and oiling the perches with kerosene will tend to keep the 
pests in check. If a poultry house becomes badly infected, it should 
be cleaned thoroughly, ever>^ part whitewashed, and the poultr}^ dust- 
ed with either insect-powder or sodium fluoride. 

The Mallophaga is a small order. Professor V. L. Kellogg in his 
"Mallophaga" (Kellogg '08 b) estimates the number of known species 
to be 1250; these represent twenty-seven genera. But there are 
doubtless many species not yet discovered, as comparatively few 
birds and mammals have been thoroughly searched for these pests. 

The work just quoted is the latest and most complete systematic 
treatise on this order. It followed a long series of papers on these 
insects published by this author. A more generally accessible ac- 
count of the species that have been found in North America is a 



MALLOPHAGA 



337 



chapter in Professor Herbert Osborn's "Insects Affecting Domestic 
Animals" (Osborn '96). 

The chief divisions of the order adopted by Kellogg ('08 b) are as 
follows. 

A.. With filiform, 3- or 5-segmented, exposed antennas; no maxillary palpi; 

mandibles vertical Suborder Ischnocera 

B. With 3-segmented antennae; tarsi with one claw; infesting mammals. 

Family Trichodectid.e 

BB. With 5-segmented antennee; tarsi with two claws; infesting birds 

Family Philopterid^s 

AA. With clavateor capitate, 4-segmented, concealed antennae; with 4-segmented 

maxillary palpi; mandibles horizontal Suborder Amblycera 

B. Tarsi with one claw; infesting mammals Family Gyropid^ 

BB, Tarsi with two claws; infesting birds, excepting a few species that infest 
kangaroos, wallabies, and wombats Family Liotheii.-^ 




CHAPTER XVII 
ORDER EMBIIDINA=' 



The Embiids 

This order is composed of small and feeble insects in which the body 
IS elongate and depressed. The winged members of the order have two 
pairs of wings, which are quite similar in form and structure; they are 
elongate, membranous, extremely delicate, and folded on the back when 
at rest; the venation of the wings is considerably reduced. The mouth- 
parts are formed for chewing. Cerci are present and consist each of two 
segments. The metamorphosis is of a peculiar type. 

This is a small order of insects; Enderlein ('12 a) in his monograph 
of the Embiidina of the world lists only sixty-one species. The body 
is elongate and depressed (Figs. 387 and 388). Only the males are 
winged ; and in some genera this sex also is 

wingless. The venation of the wings is re- ■ """ ; 

duced; this reduction has been brought •'"' 




Fig- 3^7- — Embia sabulosa, male. (After En- 
derlein.) 



Fig. 388. — Embia sabulosa, 
female. (After Enderlein.) 



about both by the coalescence of veins and by the atrophy of veins. 
Each of the veins of the wings extends along the middle of a brown band ; 
between these bands the membrane of the wing is pale in color. The 
alternating brown and pale bands give the wing a very characteristic 

*Embiidina: Embiidae, Embia, embios (ffi^ios), lively. 

(338) 



RMBIIDINA 



339 



appearance (Fig. 389). In those forms where the venation of the wings 
has been reduced by the atrophy of veins, the brown bands persist 
after the veins have faded out; hence it is easy to determine by these 
bands the former position of veins that have been lost. A discussion 
of the venation of the wings of the Embiidina is given in my "The 
Wings of Insects." 

The antennae are fiHform and are composed of from sixteen to 
thirty-two segments. The compound eyes consist of many ommatidia, 




Fig. 389. — Fore wing of Oligoloma saundersi: A, the wing; B, outline of the wing 
showing the existing venation; C, outline of the wing showing the venation 
restored. (After Wood-Mason.) 

which are of the eucone type. Ocelli are always wanting. The 
mouth-parts are mandibulate; the maxillary palpi are five-jointed 
and the labial palpi three-jointed. The abdomen is composed of ten 
distinct segments and bears at its tig a pair of two-jointed cerci. 

Figure 387 represents the male of Embia sabulosa, with the wing 
of one side removed; and Figure 388, the female of this species. 

The metamorphosis is of a type intermediate between gradual and 
complete. This was shown by Melander ('02 b), who vStudied the 
development of Embia texdna. The }^oung resemble the adults in 
the form of the body, except that the body is cylindrical instead of 
depressed; and the cuticula of the young is less densely chitinized 
and pigmented than is that of the adult. In the case of the females 



340 AN INTRODUCTION TO ENTOMOLOGY 

and of those males that are wingless in the adult instar, it might be 
said that these insects develop without metamorphosis. But in the 
case of the winged males the development resembles that of insects 
with a complete metamorphosis in one important respect; that is, 
the development of the wings is internal until the penultimate molt 
is reached. Melander states that he sectioned the fully grown larva 
and found the wings as large invaginated pockets completely beneath 
the hypodermis. In the penultimate instar of the winged females 
there are well-developed, external wing-pads. This instar may well 
be termed a pupa. 

The embiids are very active insects both in running and in flight. 
They are often gregarious. They live in silken nests or galleries under 
stones or other objects lying on the ground, and burrow into the soil 
when the surface becomes too dry. Imms found in his studies of 
Embia major in the Himalayas that maternal care on behalf of the ova 
and larvae is strongly exhibited by the females, in much the same 
.manner as is known to occur among the Dermaptera. 

Writers differ as to the source of the sillv of which the nests are 
made. Melander ('02 a) and others have described glands in the 
metatarsi of the forelegs, which open through hairs, and have ob- 
served that in spinning its nest the insect uses its fore feet. But 
Enderlein maintains that the chief source of the silk is from glands 
that open through a spinneret on the labium, although the secretion 
of the metatarsal glands may play a part in the formation of the 
silken tissues. 

The embiids are widely distributed in the warmer parts of the 
world. A few species have been found in Florida, Texas, and 
California. 



CHAPTER XVIII 
ORDER THYSANOPTERA* 

The Thrips 

The members of this order are minute insects with wings or wingless. 
The winged species have four wings; these are similar in form, long, 
narrow, membranous, not plaited, with but few or with no veins, and 
only rarely with cross-veins; they are fringed with long hairs, and in 
some species are armed with spines along the veins or along the lines 
from which veins have disappeared. The mouth-parts are formed for 
piercing and sucking. The tarsi are usually two-jointed and are bladder- 
like at the tip. The metamorphosis is gradual, but deviates from the 
usual type. 

These insects are of minute size, rarely exceeding 2 mm. or 3 mm. 
in length. They can be obtained easily, however, from various flowers, 
especially those of the daisy and clover. Ordinarily it is only necessary 
to pull apart one of these flowers to find several thrips. They are in 
many cases very active insects, leaping or taking flight with great 
agility. In case they do not leap or take flight when alarmed, they 
are apt to run about and at the same time turn up the end of the 
abdomen in a threatening manner, as if to sting. In this respect they 
resemble the rove-beetles. 

The body is long (Fig. 390). The head is narrower than the thorax, 
without any distinct neck. The antenuce are filiform or moniliform 
and consist of from six to nine segments ; they 
are alwaj'S much longer than the head and may 
be two or three times as long. The compound 
eyes are large, with conspicuous facets, which 
are circular, oval, or reniform in outline. Three 
ocelli are usually present in the winged forms, 
but sometimes there are only two ocelli ; wing- 
less species lack ocelli. The mouth parts are 
fitted for piercing and sucking ; they are in the 
form of a cone which encloses the piercing or- 
gans. The cone is composed of the clypeus, . . , . 

labnmi, maxillary sclerites, and labium. The ^^' ^^^' "^^' 

piercing organs consist of the left mandible (the right mandible is 
vestigial) and the two maxillae. Each maxilla is composed of two 
parts: first, the palpus-bearing maxillary sclerite; and second, the 
maxillary seta. For detailed accounts of the mouth-parts see Hinds 
('02) and Peterson ('15). The above statement regarding the mouth- 
parts is based on the paper by Peterson. The mouth-parts of the 
Thysanoptera bear a striking resemblance to those of the Hemiptera 

*Thysan6ptera: ihysanos (dvaavos), fringe; pteron {irr^f^bv), a wing. 

(341) 




342 AN INTRODUCTION TO ENTOMOLOGY 

and the Homoptera, which are described in detail in later chapters. 
The three thoracic segments are well developed. The wings are 
laid horizontally on the back when not in use; they are very narrow, 
but are fringed with long hairs (Fig. 391), which, diverging in flight, 
compensate for the smallness of the membrane. The fringing of the 
wings suggested the name Thysanoptera, by which the order is known 
The two longitudinal veins that traverse the disk of the wing in 




Fig. 391. — Fore wing of Mlothrips nasturlii. (After Jones.) The lettering is original. 

the more generalized forms I believe to be the radius and the media 
respectively. The costal vein is continued by an ambient vein, which 
margins the entire preanal area of the wing (Fig. 391, am). The 
ambient vein is termed the "ring vein" by writers on this order, al- 
though the term ambient vein has been long in use for veins in this 
position. There is a short longitudinal vein separating the anal and 
preanal areas; this is doubtless the anal vein (Fig. 391, A). An organ 
for uniting the two wings of each side, and consisting of hooked spines 
situated near the base of the wings and a membranous fold on the under 
side of the anal area of the fore wing, is described byHinds ('02). 

In some species one or both sexes are wingless in the adult state; 
and in others, short-winged forms occur. 

The legs are well developed, but are furnished with very peculiar 
tarsi. These are usually composed of two segments; the last seg- 
ment terminates in a cup-shaped or hoof-like end and is usually 
without claws. Fitted into the cup-shaped end of the tarsus there is 
a very delicate, protrusile, membranous lobe or bladder, which is 
withdrawn into the cup when not in use but is protruded when the 
tarsus is brought into contact with an object. This is one of the 
most distinctively characteristic features of the members of this order. 
It was this feature that suggested the name Physopoda which is ap- 
plied to this order by some writers.* 

The abdomen consists of ten distinct segments. The form of the 
caudal segments differs in the two suborders as indicated below. 

The manner of oviposition differs in the two suborders. In the 
Terebrantia the female cuts slits with her saw-like ovipositor and 
deposits her eggs singly in the tissue of the infested plant. In the 
Tubulifera it is evident that the eggs must be deposited on the surface. 

*Physopoda: physao {(pvcrdu), to blow up; pons (tows), a foot. 



THYSANOPTERA 



343 



The metamorphosis of these insects is in some respects peculiar; 
but it conforms more closely to the paurometabolous type than to 
any other, the newly hatched young resembling the adult in the 
form of its body (Fig. 392, A) and in having similar mouth-parts and 
food habits. The first two or three instars have no external wings; 
these instars are commonly referred to as larvcB. The use of the term 
larva in this connection is not inappropriate if the wings are de- 
veloping internally during these early stadia. That this may be the 
case is indicated by the large size of the wing-pads when they first 






Fig. 392. — Immature forms of the citrus thrips: A, first larval instar ; B, second 
larval instar; C, propupa; P, pupa. (After Horton.) 

appear externally. After the last larval molt the insect assumes a 
form known as the propupa (Fig. 392, C). This resembles the larva 
in form ; the antennae are slender, and the insect is moderately active. 
Its most striking feature is the presence of large wing-pads, which 
extend at first to about the end of the second abdominal segment and 
increase in length somewhat during this stadium. With the next 
molt the insect becomes what is known as the pupa. In this stage 
the wing-pads are longer (Fig. 392, D), the antennee extend back 
over the head and prothorax, and the insect is quiescent. With the 
next molt the adult form is assumed. 

The different species of thrips vary greatly in habits, some being 
injurious to vegetation, while others are carnivorous, feeding on 
aphids and other small insects, the eggs of insects, and mites, es- 
peciall}^ the "red spider." Their most important economic role, how- 
ever, is that of pests of cultivated plants. The thrips that infest 
plants puncture the tissue of the plant by their piercing mouth-parts 
and suck out the sap. 

The order Thysanoptera is divided into two suborders, which can 
be separated as follows : 

A. Female with a saw-like ovipositor; terminal abdominal segment of female 

conical; that of the male bluntly rounded Terebrantia 

AA. Female without a saw-like ovipositor; terminal abdominal segment tubular 
in both sexes, p. 345 Tubulifera 



344 



AN INTRODUCTION TO ENTOMOLOGY 



Suborder TEREBRANTIA* 

In this suborder the female has a four-valved, saw-Hke ovipositor; 
the terminal abdominal segment of the female is conical ; that of the 
male bluntly rounded. Wings are usually present; the front wings 
are stronger than the hind wings and usually have more or less well- 
developed veins; the membrane of the wings is clothed with micro- 
scopic hairs. 

The members of this suborder are more agile than those of the 
other one. They run rapidly; and spring, by bending under the tip 
of the abdomen and suddenly straightening it out. 

This suborder includes two families. 




Fig- 393- — Fore wing of Erythrothrips arizonce. 
(After Moulton.) 



Family ^OLOTHRIPID^ 

In this family the wings are comparatively broad. Each fore 
wing has two longitudinal veins extending from its base to near the tip, 
where they unite 

with a prominent - / /^^z^i^Z^ 

ambient vein 
on each side 
of the tip (Fig. 
391) ;four or five 
cross-veins are 
present in each 
fore wing, in 
some species 
(Fig. 393); in 
others, cross- 
veins are want- 
ing (Fig. 391). The ovipositor is upcurved. 

Comparatively few species belonging to this family have been 
found in our fauna; the best-known one is the following. 

The banded thrips, ALolothrips fascidtus.- — -This species is widely 
distributed both in this country and in Europe. The adult is yellow- 
ish brown to dark brown in color, with three white bands on the wings, 
one at the base, one m the middle, and one at the tip. The larva is 
yellow with the abdomen deeper orange behind. This species infests 
many plants; it is common in the heads of red clover. 

Family THRIPID^ 

In this family the wings, when present, are usually narrow and 
pointed at the tip. The radius and cubitus of the front wings, when 
present, usually coalesce for about one third their length, so that 
cubitus appears to be a branch of radius. The ovipositor is down- 
curved. 

To this family belong most of the species of thrips that have at- 
tracted attention on account of their economic importance. The 
better-known of these are the following. 

*Terebrantia : terebro, to bore through. 



TH YSA NOP TERA 345 

The onion thrips, Thrips tabdci. — This is a serious pest of the onion. 
It is found on the bulbs in loose soil and at the axils of leaves, causing 
the disease known as white blast on account of the whitish appearance 
of the infested fields. Although called the onion thrips, it infests a 
great variety of plants. 

The greenhouse thrips, Heltothrips hmnorrhoidalis . — This is a 
tropical insect, which is often a serious pest in greenhouses; it is also 
found out of doors in the milder California climate. Drops of a 
reddish fluid which turns black cover the infested leaves. 

The bean thrips, Heliothrips fascidtus.- — This is a serious pest on 
oranges, alfalfa, pear trees, and various garden crops in California. 

The orange thrips, Euthrips citri. — This is a serious orange pest in 
California and Arizona ; it deforms the new growth of foliage and causes 
scabbing and scarring of the fruits. 

The pear thrips, Euthrips pyri. — This thrips infests pears, prunes, 
peaches, and other deciduous fruits, both in California and in the 
East. It infests the opening buds and blossoms, stunting the leaves 
and blasting the blossoms. 

The tobacco thrips, Euthrips fusctis . — This is a destructive enemy 
of shade-grown tobacco causing the injury known as white vein. 
The white veins of the leaves show in the wrapper when manufactured 
into cigars. 

The strawberry thrips, Euthrips trltici. — This species was first 
described as a pest of wheat, hence its specific name; but on account 
of its extensive injury to the flowers of strawberry it is now known as 
the strawberry thrips. It is found in the flowers of almost all wild 
and cultivated plants and is the commonest and most widely distribut- 
ed of all American species of thrips. 

The grass thrips, Andph: thrips stridtus. — This species infests June 
grass, timothy, and other grasses by destroying the heads of the 
infested plants. The young insect pierces the stem just above the 
upper node, where it is tender, causing it to shrivel and all the parts 
above the injury to die. The dead and yellow heads of grasses thus 
destroyed can be seen in early summer every^where in grass-growing 
regions. This disease is known as silver-top. 

Control. — Thrips are destro3^ed in those cases where it is prac- 
ticable to spray the infested plants by the use of contact poisons, such 
as nicotine or kerosene emulsion, and soap solution. Detailed di- 
rections for making and applying these sprays are given in many 
published bulletins and in special text-books. The burning of old 
grass in early spring would probably destroy the hibernating grass 
thrips. 

Suborder TUBULIFERA* 

In this suborder the female is without a saw-like ovipositor and 
the terminal abdominal segment is tubular in both sexes. The wings 
are usually present ; the fore pair only with a single vestigial, longi- 

*Tubulifera: tubulns, a little tube; Jero, to bear. 



346 AN INTRODUCTION TO ENTOMOLOGY 

tudinal vein; the membrane of the wings is not clothed with micro- 
scopic hairs. This suborder includes a single family. 

Family PHLCEOTHRIPID^ 

The members of this family are, as a rule, considerably larger and 
more powerfully formed than the Terebrantia, some of them being 
the giants of the order. They live usually in secluded places, as be- 
tween the parts of composite flowers, under the bark of trees, on the 
underside of foliage, in galls, moss, turf, fungi, etc. Their movements 
are very deliberate and they never run or spring (Hinds '02). 

Nearly as many species and genera of this family have been found 
in this country as of the other suborder; but this family appears to 
be of much less economic importance than is the Thripidse. One 
species, Aleurddothripsfasciapennis, which is common in Florida, feeds 
on the eggs, larvae, and pup^ of the citrus white fly, Dialeurodes citri. 



CHAPTER XIX 
ORDER ANOPLURA* 

The Tnie Lice 

The members of this order are wingless parasitic insects with piercing 
and sucking mouth-parts. Their development is without metamorphosis. 

The order Anoplura is composed of the true lice. These are small 
wingless insects, which live on the skin of mammals and suck their 
blood. They are sharply distinguished from the Mallophaga or bird- 
lice by the possession of piercing and sucking mouth -parts. The most 
familiar examples of the Anoplura are three species that infest man 
and several species that are found on domestic animals. 

The name Siphunculata was proposed for this order by Meinert 
in 1 89 1 and is now used by some authors; but the name Anoplura is 
much the older name, having been proposed by Leach in 181 5, and 
is more generally used. 

The body is more or less flattened (Fig. 394). The head is free 
and horizontal. The compound eyes are vestigial or are wanting. 
There are no ocelli. The antennas are three-, four-, or five- jointed. 
The mouth is furnished with a fleshy, unjointed proboscis, which can 
be withdrawn into the head or extended to a considerable length. 
Within this proboscis are two knife-like stylets; and at its base, 
when extended, there is a wreath of recurved hooks. These hooks 
serve to anchor firmly the proboscis when inserted in the skin of the 
infested animal. Authors do not agree as to the homologies of the 
different mouth -parts of these insects. 

The thoracic segments are fused. The legs are similar; the tarsi 
consist of a single segment, which is often greatly reduced. There is 
a single tarsal claw, which is opposed by a toothed projection of the 
tibia, forming an efficient organ for clinging to the hairs of the host. 
The abdomen consists of nine segments; there are no cerci. 

The eggs of the true lice are commonly known as "nits." Thej'' 
are attached to the hairs of the host by a glue-like substance. The 
young lice resemble the adults except in size. As with the Mallophaga, 
the ametabolous condition of these insects is beheved to be an ac- 
quired one, a result of their parasitic life. 

This is a small order. Dalla Torre ('08) in his monograph of the 
Anoplura of the world lists only sixty-five species. These represent 
fifteen genera, which are grouped in four families. The two following 
families include all of the species that infest man and the common 
domestic animals. 



*Anoplura: anoplos (AkottXcj) , unarmed; our a {piipd), tail. 
(347) 



AN INTRODUCTION TO ENTOMOLOGY 



Family PEDICULID^ 

In this family the eyes are comparatively large, convex, and dis- 
tinctly pigmented; and the proboscis is short, hardly reaching the 
thorax. Here belong the three well-known species of lice that are 
parasites of man. These are the following. 

The head-louse, Pediciilus capitis. — This is the most common 
species infesting man. It lives in the hair of the head, and is most 
common on the heads of neglected children. Under ordinary circum- 
stances, cleanliness and the use of a fine-toothed comb are all that is 
necessary to insure freedom from this disgusting pest. But sometimes 
adults of most cleanly habits become infested by it. It can be 
destroyed by the use of tincture of larkspur or a larkspur lotion, 
which can be obtained from druggists. 

The body-louse, Pediculus corporis. — This insect lives upon the 
skin of most parts of the body, but especiaUy on the chest and back. 
It is often troublesome on ships, in military camps, in prisons, and 
in the apartments of uncleanly people who neglect to change their 
clothes. It was a terrible scourge during the World War, when troops 
were obliged to live under most unsanitary conditions in trenches and 
camps. The female attaches her eggs to fibers in the seams of under- 
garments, from which the young hatch in about a week. This species 
is exceedingly prolific. It and the preceding species transmit several 
human diseases, including typhus fever, trench fever, and relapsing 
fever. 

The method of destroying these vermin commonly employed in 
hospitals and poorhouses is to rub mercurial ointment in the seams 




Fig. 394. — The short- 
nosed ox-louse. (From 
Law.) 





Fig. 395. — The horse- 
louse. (From Law.) 



Fig. 396. — The hog- 
louse. (From Law.) 



of undergarments. During the World War much attention was de- 
voted to the problem of control of this pest and hundreds of papers 
were published on this subject. It has been found that both the lice 
and their eggs are destroyed by the ordinary laundering process used 
in washing clothes. 



ANOPLURA 



349 



The crab-louse, Phthtrius pubis.- — The common name of this spe- 
cies is suggested by the form of the bod}% which is nearly as broad as 
long. When highly magnified, the resemblance of this insect to a 
crab is quite striking ; but to the unaided eye it appears more like a 
large scale of dandruff. These offensive vermin affect the pubic 
region and armpits of man, stretching themselves out flat, holding 
tight to the cuticle, and inflicting most irritating punctiires. They 
can be destro^'ed b\' mercurial ointment. 



Family H^MATOPINID^ 

In this family the eyes are vestigial or wanting and the proboscis 
is very long. Here belong the true lice that infest our common domes- 
tic animals; the more important of these are the following. 

The short -nosed ox-louse, HcEmatopmus eurysternus (Fig. 394). 
The horse-louse, Hmnatoptmis asini (Fig. 395). 
The hog-louse, Hcematophius suis (Fig. 396). 
The long-nosed ox-louse, Linognathus vthtli (Fig. 397). 
The dog-louse, Linognathus piliferus (Fig. 398). 
For the destruction of these pests upon cattle, poisonous sub- 
stances must not be used, as injury would result from the animals 
licking themselves. They 
may be safely treated by 
washing with a strong in- 
fusion of tobacco leaves, or 
by rubbing with an oint- 
ment made of one part sul- 
phur and four parts lard, or 
by sprinkling with Scotch 
snuff or powdered wood- 
ashes. Stavesacre lotion 
and larkspur lotion are also 
used. The insecticide should 
be applied thoroughly, 
leaving no spot untouched 
where the lice can gather 
and remain and from which 
they can spread over the 
body again. The applica- 
tion should be repeated several times at intervals of three or four days, 
in order to destroy the young which may hatch after the first applica- 
tion. It is also necessary, in order to make sure of eradicating the 
pests, to dress with similar agents, or with strong lye or kerosene, all 
places where the cattle have been in the habit of rubbing, and the 
cracks in the stables where they have stood; or to whitewash the 
stables and rubbing-places. 

For a more extended account of the true lice found in North 
America, see Professor Herbert Osbom's "Insects Affecting Domestic 
Animals," pp. 164-188 (Osborn '96). 





Fig. 397.— The 
long-nosed ox- 
louse. (From 
Law.) 



^V^"^ 



Fig. 398.— The dog- 
louse. (From Law.) 



CHAPTER XX 
ORDER HEMIPTERA* 

The True Bugs 

The winged members of this order have jour wtngs; the first pair of 
wings are thickened at the base, with thinner extremities which overlap 
on the back. The mouth-parts are formed for piercing and sucking; the 
beak arises from the front part of the head. The metamorphosis is gradual. 

People who know but little regarding entomology are apt to apply 
the term bug to any kind of insect ; but strictly speaking, only mem- 
bers of the order Hemiptera are bugs. 

The bugs are very common insects. Many species abound on grass 
and on the foliage of other plants; some species live on the surface of 
water; others live within water; and a few are parasitic on birds and 
mammals. 

This order is a ven^ important one; it includes many species in- 
jurious to vegetation ; among these are some of our more important 
pests of cultivated plants. On the other hand, some of the species 
are ranked among beneficial insects on account of their predac'ous 
habits; for many of them feed upon noxious insects. 

The name Hemiptera was suggested by the form of the front 
wings. In these the basal half is thickened so as to resemble the 
elytra of beetles, only the terminal half being wing-like. The hind 
wings are membranous, and are folded beneath the front wings. On 
this account the front wings are often termed wing-covers; they are 
also termed hemelytra, a word suggested by their structure. 

Formerly, when the Homoptera was included in the order Hemip- 
tera, the true bugs constituted the suborder Heteroptera; this name 
indicated the remarkable difference in the texture of the two pairs of 
wings of the true bugs and served to contrast this condition with that 
found in the Homoptera, where the two pairs of wings are usually 
similar in structure. 

In the Hemiptera the front wings present characters much used 
in the classification of these insects ; and consequently special names 
have been applied to the diif erent parts of them The thickened basal 
portion is composed of two pieces joined together at their sides; one 
of these is narrow and is the part next to the scutellum when the 
wings are closed; this is distinguished as the clavus (Fig. 399, cl) ; the 
other part is the corium (Fig. 399, co). The terminal portion of the 
front wing is termed the membrane (Fig. 399, m). In certain families, 
the Anthocoridas for example, a narrow piece along the costal margin 
of the wing is separated by a suture from the remainder of the 

*Hemiptera: hemi- (vixi), half; pteron {■KTepbv), a wing. 

The order Hemiptera as now restricted includes only one of the suborders of 
the old order Hemiptera, the suborder Heteroptera. The following order, the 
Homoptera, was formerly regarded as a suborder of the Hemiptera. 

(350) 



HEMIPTERA 



351 



corirnn; this is the embolium (Fig. 400, e). In certain other cases, as 
the Miridse for example, a triangular portion of the terminal part of 




Fig. 399. — Diagram of a front wing of 
a bug: cl, clavus; co, coriuin; m, 
membrane. 



Fig. 400. — Diagram of a front wing of 
an anthocorid: e, embolium. 




the corium is separated as a distinct piece; this is the cuneus (Fig. 
401, cu). 

The wings of the Hemiptera exhibit remarkable departures from 
the primitive type of wing-venation. So great are these that, at 
first, one sees very little in com- 
mon between the wings of a 
bug and those of insects of any 
other order. But an examina- 
tion of the tracheation of the 
wings of nymphs of bugs shows 
that these wings are merely 
modifications of the primitive 
type of insect wings. This is 
more obvious in some families 

than in others; it is well shown Fig- 401.— Diagram of a front wing of a 
in the tracheation of a fore ™"^= "'• ^""^"^• 
wing of a pentatomid nymph 
(Fig. 402). 

The head in the Hemiptera varies greatly in form in the different 
families; but the accompanying figures of the head of one of the 
Belostomatidas, Lethocerus (Figs. 403 and 404), will serve to illustrate 
the position and form of the parts that are commonly referred to in 
descriptions of members of this order. 

There are two factors which make difficult the determination of 
the areas of the surface of the head in these insects that have been 
recognized and defined in the more generalized insects (see pages 3 7 
to 40) : first, in some cases the sutures that limit these areas in the 
more generalized insects are here obsolete; second, the basal part of 
each mandible and of each maxilla enters into the composition of the 
wall of the head. 

A similar modification of the head and mouth-parts exists in the 
Hoinoptera, and the students of the Hemiptera should study the 
relations of the mouth-parts to the head -capsule in that order, where 
they are more easily seen than in the Hemiptera. 



S52 



AN INTRODUCTION TO ENTOMOLOGY 



An important feature of the head in the Hemiptera is the extended 
development of the gular regions, which results in the beak being 




Fig. 402. — Tracheation of a fore wing of a pentatomid nymph. 

borne by the front part of the head. This contrasts strongly with the 
condition found in the Homoptera, where the gula is so reduced that 




Fig. 403. — Head of Lemocertis, aorsal Fig. 404.^ — Head of Lethocerus, ventral 
aspect. asoect. 

the beak arises from the hind part of the lower side of the head. 

In Lethocerus the occiput (Fig. 403, o) is separated from the vertex 

by a distinct transverse suture. The vertex (Fig. 403, v, v) is very 



HEMIPTERA 353 

short on the middle Hne of the body but is much longer on each side 
next to the compound eye ; the epicranial suture is very indistinct in 
the adult. In those bugs in which the paired ocelli are present they 
are borne by the vertex. Immediately in front of the vertex is the 
front or frons (Fig. 403, /). The clypeus is a narrow, elliptical sclerite 
which is well defined (Fig. 403, c). Some writers on the Hemiptera 
and Homoptera term the ch'peus the tylns; but, for the sake of 
uniformity, the use of this name should be discontinued. 

The four regions of the head referred to in the preceding paragraph, 
the occiput, the vertex, the front, and the clypeus, are easily homol- 
ogized with the corresponding regions in the more generalized insects. 
We will now consider certain modifications of the structure of the 
wall of the head that are correlated with the development of the type 
of mouth-parts characteristic of the Hemiptera and Homoptera. 

On either side of the clypeus there is what appears to be a pro- 
longation of the front. In Lethocerus (Fig. 403, x, x), each of these 
prolongations extends about half the length of the clypeus and 
bounds the eye in front. It is believed that each of them represents 
the basal part of a mandible; they are termed, therefore, the mandibu- 
lar sclerites. In some Homoptera the mandibular sclerites are dis- 
tinct ; this condition exists in the head of a cicada figured in the next 
chapter (Fig. 463). The mandibular sclerites were so named by 
Smith ('92), who first recognized that they pertain to the mandibles. 
Before that time several different names were applied to them, which 
are still in use by some writers; these are jugcB, lorcB, and fulcra. 

In Lethocerus there is a pair of sclerites in front of the mandibular 
sclerites and bounding the distal end of the clypeus; each of these is 
the basal part of a maxilla; for this reason they are termed the 
maxillary sclerites (Fig. 403, y, y) In Lethocerus the tips of these 
sclerites meet on the dorsal wall of the head covering the tip of the 
clypeus. 

On the ventral aspect of the head, the gula occupies the median 
area (Fig. 404, gu); and the gen(Z, the lateral areas (Fig. 404, ge). 
In each gena there is a deep groove in which the very remarkable 
antenna rests. 

At the front end of the ventral wall of the head there is a pair of 
sclerites, each of which is articulated with a maxillary sclerite; these 
are known as the bucculce and are believed to represent the maxillary 
palpi (Fig. 404, bu). In Lethocerus the caudal margin of each buccula 
is solidly joined to the front end of the gula. 

From the above account it can be seen that only a portion of 
the mouth-parts enters into the constitution of the beak. The beak 
consists of the following parts: the labrum, the labium, and four very 
slender lancet-like organs enclosed in the labrum and labivim, the 
mandibular setae and the maxillary setae. 

The labrum is joined to the distal end of the clypeus ; in Lethocerus 
the base of the labrum is covered by the maxillary sclerites, where 
they overlap the tip of the clypeus, and its distal end extends into the 
furrow of the labiiun, but the intermediate portion is exposed 



354 



AN INTRODUCTION TO ENTOMOLOGY 



(Fig. 403, /). It is a slender, pointed, transversely striated organ. 
The Icoium constitutes the most prominent part of the beak; in 
most Hemiptera it consists of four segments ; 
but in several families it is reduced to three 
segments. At the distal end of the third 
segment in Lethocerus and some other aquatic 
Hemiptera there is a pair of small append- 
ages, each of which consists of a single seg- 
ment (Fig. 403, Ip); these were described 
by Leon ('97) as vestiges of the labial palpi.* 
The dorsal surface of the labium is deeply 
grooved, forming a channel which encloses 
the mandibular and maxillary set^e. The 
labiimi is not a piercing organ; its function 
is to protect and direct the sets and to de- 
termine, by means of tactile hairs at its tip, 
the place where the puncture should be made 
by the setae (Fig. 405, t). 

The mandibular setos and the maxillary 
setcB are four slender, lance-like organs 
which arise within the head-capsule and pass 
out from the head through a furrow in the 
lower side of the la- 
brum and extend in 
a furrow on the upper m 

side of thelabiimito 
the tip of this organ, 
from which they are 
pushed out when not 
in use (Fig. 405). As 
the four seta3 emerge 
from the head they 
lie side by side; the 
outer pair are the mandibular setce, the inner Fig. 406. — Cross-section 
pair the maxillary setas. Farther from the head 
the maxillary setag become twisted so that one 
of them lies above the other. Figure 406 repre- 
sents a cross-section of the setae of a squash- 
bug as figured by Tower ('14); the setae are 
fastened together by interlocking grooves 

*There has been much discussion regarding the homologies of the parts of the 
labium in the Hemiptera and the Homoptera. The early entomologists believed 
that the lower lip of bugs was composed of the labium and the grown-together 
labial palpi; but this view is no longer held. Leon, who published a series of 
papers on the labium of aquatic bugs, believes that the first two segments of the 
labium consists of the submentum and the mentum; the third segment, of the 
palpiger, which bears vestiges of the labial palpi; and the fourth segment, of the 
remainder of the ligula. Heymons ('99) argues at great length against the con- 
clusions of Leon. He believes that the segmentation of the labium is merely the 
result of secondary divisions of this organ and that labial palpi do not exist in the 
Hemiptera and Homootera. 




Fig. 405. — Last segment of 
the beak of Lethocerus, 
with setae projecting : md, 
mandibular seta; mx, 
maxillary seta. 




md" 



of the setae of Anasa 
Iris'.is: md, mandibular 
setae; ot, maxillary se- 
tae; fc, food canal; sc, 
salivarv canal. (From 
Towerj 




IIEMIPTERA S55 

and ridges ; and between the maxillary setee are two canals, the upper 
one (/c) for the passage in of food, the lower one {sc) for the passage 
out of saliva. The tip of the mandibular setas are barbed (Fig. 405, 
md) ; their function is that of piercing the tissue fed upon and holding 
the seta^in place; while the tips of th'5 maxillary setse, which are acute 
and fluted, probe the tissue, take up the fluid food, and eject the saliva. 

Within the head each seta is connected with a chitinous lever, or 
with a series of two levers which in turn articulate with the head- 
capsule; the in and -out move- 
ments of the setffi are produced 
by muscles extending from the 
head-capsule to them and to 
the levers connecting them 
with the wall of the head. Fig- 
ure 407 represents the articu- 
lation of a mandibular seta of 
a squash-bug, as represented 
by Tower; and in the next 
chapter the relations of both 
the mandibular setae and the 

maxillary setae to the head- Fig- 407 •— Articulation of a mandibular 

capsule in a cicada are rep- seta with tlie wall of the head: md,man- 

J /-n- ^ \ dibular seta; c and 6, chitmous levers; g, 

resented (l^lg. 465). wall of the head; rw, retractor muscles; 

Correlated with the de- pm, protractor muscle. (From Tower.) 
velopment of the hemipterous 

type of mouth-parts there is a remarkable specialization of the phar- 
ynx, which fits it as a sucking organ, and the development of an 
organ for forcing out the saliva, which is known as the salivary pump. 
A detailed account of these organs is given by Bugnion and Popoff 
(•11). 

Most of the Hemiptera protect themselves by the emission of a 
disagreeable odor. In the adult stink-bugs (Pentatomidaj) this is 
caused by a fluid which is excreted through two openings, one on 
each side of the ventral aspect of the thorax, behind or near the middle 
coxa. These openings are termed the osteoles. Each of these is 
usually in some kind of an open channel styled the osteolar canal, 
and this is surrounded by a more or less rugged and granulated 
space, the evaporating surface. In the nymphs the stink-glands 
open on the dorsal aspect of the abdomen. In the bedbug {Cimex), 
the stink -glands open in the dorsal wall of the first three abdominal 
segments. The legs of the Hemiptera vary greatly in form, but the 
tarsi are rarely more than three-jointed. The lateral margin of the 
abdominal segments is much developed in several families, and forms 
a flat, reflexed or vertical border to the abdomen, which is called the 
connexivum. 

In the Hemiptera the metamorphosis is gradual; the newly 
hatched young resembles the adult in the form of its body but lacks 
wings. After one or two molts the wing-buds appear and become 
larger and larger at successive molts. With the last molt there takes 



356 AN INTRODUCTION TO ENTOMOLOGY 

place a great expansion of the wings, the change at this time being 
much greater than at either of the previous molts. There are many 
forms in this order in which wings are not developed. In some 
species all individuals are wingless; in others there are two forms of 
adults, the winged and the wingless. 

In this order we find variations in structure which correspond 
closely with variations in habits. There are certain families the 
members of which are truly aquatic, living within the water, through 
which they swim and to the surface of which they come occasionally 
for air. There are others which are truly terrestrial, living upon the 
surface of plants, or in other positions away from water. There are 
still other families the members of which hold an intermediate position 
between the aquatic and the terrestrial forms, living upon the surface 
of water or in marshy places. 

In the systematic arrangement of the families of the Hemiptera 
adopted here the aquatic forms are placed first; the terrestrial forms, 
last; and the semiaquatic forms hold an intermediate position. The 
sequence of the families is more fully indicated in the following 
synopsis. 

SYNOPSIS OF FAAIILIES 

The Short-horned Bugs. Bugs with short antennae, which are nearly or quite 

concealed beneath the head. 
Bugs that live within water. 

The Water- boatmen, Family Corixid^. p. 360. 
The Back-swimmers, Family Notonectid^. p. 362. 
The Water-scorpions, Family Nepid^. p. 364. 
The Giant Water-bugs, Family Belostomatid.e. p. 365. 
The Creeping Water-bugs, Family NaucoriDvE. p. 367. 
Bugs that live near water. 

■ The Toad-shaped Bugs, Family Gelastocorid^. p. 368. 
The Ochterids, Family Ochterid.e. p. 368. 
The Long-horned Bugs. Bugs with antennae at least as long as the head, and 

prominent except in the Phymatids, where they are concealed under the 

sides of the prothorax. 
The Semi-aquatic Bugs. 

The Shore-bugs, Family Saldid^. p. 369. 

The Broad-shouldered Water-striders, Family Veluzje. p. 369. 
The Water-striders, Family Gerrid^. p. 370. 
The Mesoveliids, Family Mesovelhd^. p. 372. 
The Hebrids, Family Hebrid^. p. 372. 
The Water-measurers, Family Hydrometrid.e. p. 373. 
The Land-bugs. 

The Land-bugs with four-jointed antenticE. 

The Schizopterids, Family Schizopterid^. p. 373. 

The Dipsocorids, Family Dipsocorid^. p. 374. 

The Isometopids, Family Isometopid^. p. 374. 

The Leaf-bugs, Family M1RID.E. p. 375. 

The TermatophyHds, Family Termatophvlid^. p. 377. 

The Flower-bugs, Family Anthocorid^. p. 377. 

The Bedbugs, Family Cimicid^. p. 378. 

The Many- combed Bugs, Family Polyctenid^. p. 379. 

The Nabids, Family Nabid^. p. 380. 

The Assassin-bugs, Family Reduvud^. p. 380. 

The Ambush-bugs, Family Phymatid^. p. 382. 

The Unique-headed Bugs, Family Enicocephahd.e. p. J83. 



HEMIPTERA 357 

The Lace-bugs, Family Tingid^. p. 384. 
The Cotton-stainer Family, Family Pyrrhocorid^. p. 385. 
The Chinch-bug Family, Family Lyg^id^. p. 386. 
The Stilt-bugs, Family NeididJe. p. 388. 
The Flat-bugs, Family Aradid.e. p. 388. 
The Squash-bug Family, Family Coreid^. p. 389. 
The Land-bugs with five-jointed antennce. 

The Stink-bug Family, Family Pentatomid^. p. 390. 

The Burrower-bugs and the Negro-bugs, Family Cydnid^. p. 391. 

The Shield-backed-bugs, Family Scutellerid^. p. 392. 

TABLE FOR SEPARATING THE FAMILIES OF THE HEMIPTERA 

h.. Antenna shorter than the head, and nearly or quite concealed in a cavity 

beneath the eyes. 

B. Hind tarsi with indistinct setiform claws (except in Plea, of the family 

Notonectidse, which is less than 3 mm. in length). 

C. Fore tarsi consisting of one segment, which is flattened or shovel-shaped, 

and without claws; head overlapping the prothorax dorsally. p. 360. 

CORIXID^ 

CC. Fore tarsi of the usual form, and with two claws; head inserted in the 

prothorax. p. 362 Notonectid^ 

BB. Hind tarsi with distinct claws. 

C. Ocelli absent; bugs that live within water. 

D. Membrane of the hemelytra with distinct veins. 

E. Caudal appendages of the abdomen long and slender; tarsi one- 
segmented, p. 364 Nepid^ 

EE. Caudal appendages of the abdomen short, flat, and retractile; 

tarsi two-segmented, p. 365 Belostomatid^ 

DD. Membrane of the hemel}i;ra without veins. p. 367..NAucoRiDiE 
CC. Ocelli present ; bugs that live on shores of streams and ponds. 

D. Fore legs stout, fitted for grasping; antennae concealed, p. 368. 

Gelastocorid^ 

DD. Fore legs slender, fitted for running; antennae exposed, p. 368. 

OCHTERIDiE 

AA. Antennae at least as long as the head, usually free, rarely (P hymatidae) 
fitting in a groove under the lateral margin of the pronotum. 
B. Body linear; head as long as the three thoracic segments, p. 373. 

Hydrometrid^ 

BB. Body of various forms, but, when linear, with the head shorter than the 

thorax. 

C. Last segment of the tarsi more or less split, and with the claws of at 

least the front tarsi inserted before the apex. 

D. Hind femora extending much beyond the apex of the abdomen; 

intermediate and hind pairs of legs approximated, very distant 

from the front pair; beak four-jointed, v. 370 Gerrid^ 

DD. Hind femora not extending much beyond the apex of the ab- 
domen ; intermediate pair of legs about equidistant from front 
and hind pairs (except in Rhagovelia) ; beak three-jointed. 

p. 369 VeliidvE 

CC. Last segment of the tarsi entire, and with the claws inserted at the 
apex. 
D. Antennse four- jointed.* 

E. Hemelytra resembling network, and very rarely with any dis- 
tinction between the corium and the membrane, p. 384. 

TlNGID^ 

EE. Hemelytra of various forms or absent, but not of the form 
presented by the Tingidae. 

*In certain families there are minute intermediate joints between the principal 
joints of the antennae; for the purposes of this table, these intermediate joints 
are not. counted. 



358 AN INTRODUCTION TO ENTOMOLOGY 

F. Beak three-jointed. 
G. Hemelytra when well-developed with an emboLam (Fig. 
408); those forms in which the adult has vestigial 
hemelytra have no ocelli. 
H. Hemelytra vestigial; parasitic bugs preying on man, 

bats, and birds, p. 378 Cimicid.^ 

HH. Hemelytra usually well developed; not parasitic 

bugs. p. 377 Anthocorid^ 

GG. Hemelytra when well developed without an embolium; 
those forms in which the adult has vestigial hemely- 
tra have ocelli. 
H. Ocelli wanting. 

I. Body greatly flattened, p. 388 Aradid^ 

II. Body not greatly flattened, p. 38o..Reduviid^ 
HH. Ocelli present, though sometimes difficult to see. 

I. Antennas whip-like, the first two segments 

short and thick, the third and fourth long and 
very slender and clothed with long hairs, the 
third segment thickened towards the base. 
J. Head when viewed from above wider than long, 
strongly deflexed; beak short, p. 373. 

SCHIZOPTERID^ 

JJ. Head extended horizontally or slightly de- 
flexed; beak long. p. 374. . . Dipsocorid^ 

II. Antennae not of the form described above. 

J. Beak long, reaching to or beyond the inter- 
mediate coxag. 
K. Membrane of hemelytra with looped veins. 

p. 369 Saldid^e 

KK. Alembrane of hemelytra without veins. 

L. Hemelytra with the clavus similar in 

texture to the membrane (Fig. 409). 

p. 372 Hebrid^ 

LL. Clavus and membrane distinct, p. 

372 Mesoveliid^ 

JJ. Beak not reaching the intermediate coxae. 
K. Front legs with greatly thickened fem- 
ora, p. 382 Phymatid^ 

KK. Front femora somewhat thickened, 
but much less than half as wide as 

long. p. 380 Reduviid^ 

'3F. Beak four-jointed. 

G. Front legs fitted for grasping prey. 

H. The fore tarsi, which are one-jointed, capable of be- 
ing closed upon the end of the broad tibice. p. 383. 

Enicocephalid^ 

HH. The fore tibiae armed with spines andcpable of 
being closed tightly upon the femora, wahich are 
stout. In the forms with long wings the mem- 
brane is usually furnished with four long veins 
bounding three discal cells which are often open. 
From these cells diverge veins which form sev- 
eral marginal cells (Fig. 410). p. 380..NABID.E 
GG. Front legs fitted for walking. 

H. Hemelytra with a cuneus; membrane with one or 
two closed cells at its base, otherwise without 
veins (Fig. 411). 
I. Ocelli wanting. 
J. Membrane of the hemelytra with two closed 

cells, p. 375 MiRiD.E 

JJ. Membrane with only one closed cell. 



HEMIPTERA 359 

K. Tarsi furnished with an aroHum. p. 375. 

MlRID^ 

KK. Tarsi without an aroHum. p. 377 

Termatophylid^ 

II. OcelU present, p. 374 Isometopid^ 

HH. Hemelytra without a cuneus; meinbrane with 
four or five simple or anastomosing veins aris- 
ing from the base, or with a large number of 
veins arising from a cross-vein at the base. 

I. Ocelli w£.iting. 

J. Exceedingly flat bugs, p. 388 Aradid^ 

J J. Rather stout and heavily formed bugs. p. 
385 Pyrrhocorid^ 

II. Ocelli usually present. 

J. Head with a transverse incision in front of 
the ocelli, which are always present (Fig. 
449). p. 388 Neidid^ 

JJ. Head without transverse incision. 

K. Membrane with four or five simple veins 
arising from the base of the membrane, 
the two inner ones sometimes joined to 
a cell near the base (Fig. 413). p. 386. 
LYG^IDiE 

KK. Membrane with many, usually forked 
veins, springing from a transverse 
basal vein (Fig. 414). p. 389. . . . 
CoREID/E 

HHH. Hemelytra vestigial; parasitic bugs preying 

on bats. p. 379 POLYCTENIDiE 

DD. Antennas five- jointed.* 

E . Hemelytra with the clavus similar in texture to the membrane, 
which is without veins (Fig. 409) ; small semiaquatic bugs, 
measuring less than 3 mm. in length {Hebrus). p. 372 
Hebrid^ 

EE. Hemelytra with the clavus markedly thicker than the 
membrane. 

F. Tibiae armed with strong cpines. p. 391 Cydnid^ 

FF. Tibije smooth or with small spines. 

G. Scutellum narrowed behind, only rarely almost cover- 
ing the abdomen, p. 390 Pentatomid^ 

GG. Scutellum not narrowed as in the Pentatomidag, 
very convex, nearly or quite covering the ab- 
domen, p. 392 SCUTELLERID^ 



*In some cases there are minute intermediate joints between the principal 
joints of the antennas; for the purposes of this table these intermediate joints are 
not counted. 



360 



AN INTRODUCTION TO ENTOMOLOGY 




Fig. 410. — Nabidae. 



Fig. 411. — JMiridEe. 




Fig. 412, — Pyrrhocorid^. 



Fig. 413.— Lygaeidae. 




Fig. 414. — Coreidae. 
Figures 408 to 414. — Diagrams illustrating the types of hemelytra characteristic 
of several families of Hemiptera. 

• Family CORIXID^* 



The Water-Boatmen 

The family Corixidffi includes oval, gray-and-black mottled bugs, 
usually less than half an inch in length, which live in lakes, ponds, 
and streams, in both stagnant and running water. The characteristic 
form and markings of these insects are shown in Figure 415. 

The name of the typical genus of this family, Corixa, is evidently 
from the Greek word coris, meaning a bug. For this reason many 
writers have spelled the generic name Corisa and the family name 
Corisidce. This name was probably given to these insects because 
they have an odor like that of the bedbug. 

The water-boatmen exhibit some striking peculiarities in struc- 

*Corixidae, Corixa, a misspelling of Corisa: coris («6/"s)i a bug. 



HEMIPTERA 361 

ture: the head overlaps the prothorax instead of being inserted in 
that segment; the beak is very short and scarcely distinguishable 
from the face, the opening to the mouth being on the front of the so- 
called beak; the tarsi of the front legs (termed palce) are flattened 
or scoop-like in form; each consists of a single segment and bears a 
comb-like fringe of bristles; the middle legs are long, slender, and 
end in two claws ; the hind legs are flattened and fringed for swimming ; 
and, in the males, the abdominal sterna, especially the four caudal 
ones, are very uns\Tnmetrical, being on one side broken into irregular- 
shaped fragments. 

The water-boatmen have the body flattened above, and swim 
upon their ventral surface; they differ in these respects from the 
members of the next family. They swim with a quick, darting 
motion; they use for this purpose chiefly their long, oar-like, posterior 
legs. When in their favorite attitude, they are anchored to some 
object near the bottom of the pond or aquarium by the tips of their 
long, slender, intermediate legs; at such times the fore legs hang 
slightly folded, and the posterior legs are 
stretched out horizontally at right angles to 
the length of the body. The body of these 
insects, with the air which chngs to it, is much 
lighter than water; consequently whenever 
they lose hold upon the object to which they 
have been clinging, they rise quickly to the 
surface, unless they prevent it by swimming. 
They occasionally float on the surface of the 
water, and can leap into the air from the 
water and take flight. Fig. 415.— A water-boat- 

The bodies of these insects, as they swim 
through the water, are almost completely 

enveloped in air. The coating of air upon the ventral surface and sides 
can be easily seen, for it glistens like silver. By watching the insects 
carefully when they are bending their bodies, the air can be seen to fill 
the spaces between the head and the prothorax, and between the pro- 
thorax and the mesothorax. The space beneath the wings is also filled 
with air. When these insects are in impure water, they must come 
to the surface at intervals to change this supply of air. But I have 
demonstrated that in good water it is not necessary for them to do 
this. The air with which the body is clothed is purified by contact 
with the fine particles of air in the water ; so that the insect can breathe 
its coat of air again and again indefinitely. 

It has been commonly believed that the corixids are carnivorous ; 
but Hungerford ('19) has shown, by an extended series of experiments, 
that these insects gather their food supply from the ooze at the 
bottom of pools in which they live. This flocculent material they 
sweep into their mouths by means of the flat rakes of their fore tarsi. 
This material is largely of plant origin; but the protozoa and other 
minute animals living on it are also consimied. This author also 
found that the corixids feed on the chlorophyll of Spirogyra. 




362 AN INTRODUCTION TO ENTOMOLOGY 

In most cases the eggs of corixids are attached to the stems of 
aquatic plants; but Ramphocorixa acuminata usually attaches its 
eggs to the body of a crayiish. 

The males of most of the Corixidse are furnished with stridulating 
organs. These consist of one or two rows of chitinous "pegs" on the 
fore tarsi and a roughened area on the inner surface of the fore femora 
near the base. By rubbing the tarsal comb of one leg over the 
roughened area of the femur of the opposite leg, a chirping sound is 
produced. These stridulating organs differ in form in different species. 

In addition to the stridulating organs of the fore legs there is in 
certain species a more or less currv'-comb-like organ near the lateral 
margin of the dorsal wall of the sixth abdominal segment ; this has 
been termed the "strigil." It is situated, when present, on the left 
side in Corixa and on the right side in several other genera. Its func- 
tion has not been definitely determined. 

Both the adults and the eggs of Corixa are used for food for man 
and for birds in Mexico and in EgA-pt. The eggs are gathered from 
water-plants. Glover states that in Mexico the natives cultivate a 
sedge upon which the insects will deposit their eggs; this sedge is 
made into bundles, which are floated in the water of a lake until 
covered with eggs; the bundles are then taken out, dried, and beaten 
over a cloth ; the eggs, being thus disengaged, are cleaned and powdered 
into flour. Kirkaldy ('98) reports the importation into England of 
Corixa mercenaria and its eggs for food of insectivorous birds, game, 
fish, etc., by the ton; and computes "that each ton of the adults will 
contain little short of 250 million individuals!! As to the ova, they 
are beyond computation." The adults are captured at night with 
nets when they leave the water in swarms. 

It is difficult to separate the different species of water-boatmen on 
account of their close resemblance to each other; this is especially 
true of the females. Fifty-five species are listed in the Van Duzee 
check -list; these represent six genera. 



Family NOTONECTID^ 

The Back-Swimmers 

The Notonectidae differ from all other aquatic Hemiptera in the 
fact that they always swim on their backs ; and there 
is a corresponding difference in the form of these in- 
sects. The body is much deeper than in the allied 
families, and is more boat-shaped. The back, from 
the peculiar attitude of the insect when in the water, 
■^^8- 416.— iVo/o- corresponds to the bottom of a boat, and is sloped 
necta unduLata. ^^ ^^ ^^ greatly resemble in form this part (Fig. 416). 
The eyes are large, reniform, twice sinuated on the outer side, 
and project a little way over the front margin of the prothorax. Ocelli 
are absent. The prothorax has the lateral margins sharp and pro- 




HEMIPTERA 363 

jecting. The legs are all long ; the hind pair are much the longest and 
fitted for swimming. The tarsi consist each of three segments, but 
the basal segment is so small that it is often overlooked. There is a 
ridge along the middle line of the venter which is clothed with hairs, 
and along each side of this a furrow. Along the upper edge of the 
outside of this furrow and a short distance from the side of the body, 
there is a fringe of long hairs, and beneath this fringe the abdominal 
spiracles are situated. 

The features presented by the ventral side of the abdomen just 
referred to can be seen on dead specimens; but it is well to examine 
them on living insects. This can be done by placing a back-swimmer 
in a glass of water, and, when it is resting at the surface of the water, 
studying it by means of a lens of low power. Under these conditions 
it can be seen that the furrow on either side of the venter is an air- 
chamber, which is enclosed by the two fringes of hairs, one borne 
by the ridge of the middle line on the body and the other by the 
outer margin of the furrow. It can also be seen that there is a hole 
near the tip of the abdomen through which the air passes into the 
chambers beneath the fringes of hairs. Sometimes when watching 
an individual under these conditions it will be seen to force the air 
out of the chambers beneath the fringes of hair, using the hind legs 
for this purpose, and sometimes an entire fringe will be lifted like a lid. 

By examining the first ventral abdominal segment of a dead indi- 
vidual a little furrow can be seen on each side; these are air-passages 
extending between the chambers on the ventral side of the abdomen 
to that beneath the wings. 

Air is also carried among the hairs on the lower side of the thorax, 
and in the spaces between the head and the prothorax and between the 
prothorax and the mesothorax; this is probably expired air. 

In collecting back-swimmers, care must be taken or they will inflict 
painful stings with the stylets of their beak. 

The manner of oviposition of these insects differs in different spe- 
cies. Some merely attach their eggs to the surface of aquatic plants 
by means of acolorless, water-proof glue; others have a long oviposi- 
tor by means of which they insert their eggs in the tissue of these 
plants. 

The males of some back-swimmers possess stridulating areas; 
these are located on the femora and tibiae of the fore legs and on the 
sides of the face at the base of the beak. 

The notonectids of our fauna represent three genera ; these can be 
separated by the following table : 

A. Legs dissimilar; hind legs flattened and fringed for swimminfr. 

B. Last segment of the antennas much shorter than the penultimate segment. 

NOTONECTA 

BB. Last segment of the antennae longer than the penultimate segment. 

BUENOA 

AA. Legs quite similar Plea 

Noionecta. — To this genus belong the greater number of our 
species, of which twelve have been described. These are the back- 



364 AN INTRODUCTION TO ENTOMOLOGY 

swimmers that are commonly seen floating at the surface of the water, 
with the caudal part projecting sufficiently to admit of the air being 
drawn into the air chambers. When in this position, their long, 
oar-like, hind legs are stretched outward and forward ready for action ; 
when disturbed they dart away toward the bottom of the pond, 
carrying a supply of air with them. 

Buenoa. — This genus, of which six species have been found in this 
country, is composed of much more slender forms than is the preceding. 
The habits of two of our species have been studied by Hungerford (' 1 9) . 
These insects do not rest at the surface of the water as do some species 
of Notonecta, but may be seen swimming slowly, or even poising in 
midwater some distance beneath the surface. They abound in water 
teeming with Entomostraca, upon which they largely feed. 

Plea. — The members of this genus are small insects, not exceeding 
3 mm. in length. The shape of the body is quite different from that 
of other back-swimmers, being highly arched behind. They are 
found in tangles of aquatic vegetation, to thefilaments of which they 
cling when at rest. They feed on small Crustacea. Only one species, 
Plea siriola, has been described from our fauna. 



Family NEPID^ 

The Water-Scorpions 

The members of this family can be distinguished from other 
aquatic Hemiptera by the presence of a long respiratory tube at the 
end of the abdomen. This tube consists of two long filaments, each 
with a groove on its mesal side. By applying these 
filaments together the grooves form a tube, which 
conducts the air to two spiracles situated at the 
caudal end of the abdomen. By means of this ap- 
paratus these insects are able to rest on the bottom 
of a shallow pond, or among rubbish or plants in 
water, and by projecting this tube to the surface 
obtain what air they need. 

With regard to the form of the body, two very 
different types exist in this family. In one, repre- 
sented by the genus Nepa, the body is a long oval, 
Yig.^iT.—Nepa ^^^' ^"^ ^^^^ (^^S- 4^ 7) I ^" ^^^ other, represented 
a'piculata. by the genus Ranatra, the body is almost linear and 

cylindrical (Fig. 418). An intermediate form, 
Curicta, represented by two species, is found in Louisiana, Texas, and 
Arizona. 

The water-scorpions are carnivorous; and with them the first pair 
of legs is fitted for seizing prey. In these legs the cox^ are very long, 
especially in Ranatra; the femora are furnished with a groove into 
which the tibias and tarsi fit like the blade of a pocket-knife into its 
handle. 




HEMIPTERA 



365 



Although the Nepidae are aquatic insects, the second and third 
pairs of legs are fitted for walking rather than for swimming. 

Of the genus Nepa we have only a single species, Nepa apiculdta. 
This insect is about i6 mm. in length, not 
including the respiratory tube, which 
measures a little more than 6 mm. It 
lives in shallow water concealed in the 
mud or among the dead leaves and twigs, 
lying in wait for its prey. The eggs are 
inserted in the tissues of decaying plants ; 
they are an elongate oval and bear near 
one end a crown of eleven slender fila- 
ments. 

Of the genus Rdnatra eight American 
species have been described. These in- 
sects are found in the same situations as 
Nepa; where, owing to the linear form of 
the body and to the dirt with which it is 
usually covered, it is quite difficult to de- 
tect their presence. They have also been 
observed in deep water clinging to the 
stems of rushes and grasses, with the re- 
spiratory tube piercing the surface film 
(Bueno) ; and also upon floating dead 
leaves and stalks of cat-tail, where the}' 
were basking in the sun and entirely dry 
(Hungerford). 

Ranatra has stridulating organs; these consist of a roughened 
patch on the outside of each fore coxa and a rasp on the inner margin 
of each shoulder of the prothorax ; b}' means of these organs a squeak- 
ing sound is produced. 

The eggs of Ranatra have been described by Pettit; they are 
elongate oval, about 3.5 mm. in length, and bear at one end a pair of 
slender appendages, about 4 mm. long; they are embedded in the 
rotting stems of aquatic plants, from which the appendages of the 
eggs project. 

A monograph of the Nepidfe of North America was published by 
Himgerford ('22). 




Fig. 418. — Ranatra ftisca. 



Family BELOSTOMATID^ 
The Giant Water-Bugs 



The common name "giant water-bugs" was applied to this family 
because to it belong the largest of the Hemiptera now living; a 
species that is found in Guiana and Brazil measures from 75 to 100 
mm. in length; and the larger of our species exceed in s^'ze our other 
water-bugs. 



366 



AN INTRODUCTION TO ENTOMOLOGY 




Lethocerus america- 



The members of this family are all wide and flat-bodied aquatic 
insects, of more or less ovate outline. The fore legs are raptorial ; 
the middle and hind legs are fitted for 
swimming, being flattened and ciliated; 
this is especially true of the hind legs. 
At the caudal end of the body there is, 
in the adult, a pair of narrow, strap-like 
respiratory appendages, which are re- 
tractile. 

These insects are rapacious creatures, 
feeding on other insects, snails, and small 
fish. Like other water-bugs, they fly fi om 
pond to pond and are frequently attracted 
to lights. This is especially the case where 
electric lights are used, into which they 
sometimes fly and are killed by hundreds. 
On this account they are known in many 
parts of the country as "electric-light 
bugs." 

The family Belostomatidas is repre- 
sented in this country by four genera. 
Recent studies of the nomenclature of the 
genera of this family have resulted in the 
making of changes in some of the generic 

names. This should be kept in mind when using the older text-books. 
Our genera are separated by Hungerford ('19) as follows: 
A. Mesothorax with a strong midventral keel; membrane of the hemelytra re- 
duced Abedus 

AA. Mesothorax without a midventral keel; membrane of the hemelytra not 
reduced. 

B. Basal segment of the beak longer than the second; base of the wing- 
membrane nearly or quite straight. Body about 25 mm. or less in 
length Belostoma 

BB. Basal segment of the beak shorter than the second; base of the wing- 
membrane sinuous. Body more than 37 mm. in length. 
C. Anterior femora grooved for the reception of the tibia. ..Lethocerus 
CC. Anterior femora not grooved for the reception of the tibia.. Benacus 

Lethocerus. — To this genus 
and the following one belong our 
larger members of this family. 
The appearance of these insects 
is indicated by Figure 419, which 
represents Lethocerus americdnus. 
In this genus the anterior femora 
are furnished with a groove for 
the reception of the tibia. Five 
species have been described from 
the United States and Canada. 
In most of the references to these 
insects in our literature the gener- 




Fig. 420. — Belos- 
toma fltmiinea. 



ic name Belostoma is used. 

Benacus. — Only a single spe- 




Abedus, with eggs. 



HEMIPTERA 367 

ciesof this genus, i?ewacM5 gnseus, is found in our fauna. This close- 
ly resembles Lethocerus americanus (Fig. 419), but can be distinguish- 
ed from that species by the absence of the groove in the femora of the 
fore legs. 

Belostoma. — To this genus as now recognized belong our more com- 
mon representatives of the smaller members of this family. These 
have long been known incorrectly under the generic name Zaitha. 
Our most common species is Belostoma flummea (Fig. 420). 

In this genus and the following one the eggs are carried by the 
males on their backs, where they are placed by the females, sometimes 
in spite of vigorous opposition on the part of the male. 

Abedus. — Five species of this genus have been found in the south- 
western parts of the United States. Figure 421 represents the male 
of one of these carrying his load of eggs. 

Family NAUCORID^ 

The Creeping Water-Bugs 

The Naucoridffi includes fiat-bodied, chiefly oval insects, of 
moderate size. The abdomen is without caudal appendages. The 
front legs are fitted for grasping, the femora being greatly enlarged; 
the middle and hind legs are suited for crawling rather than for 
swimming. There are no ocelli ; the antennae are very short, and well 
concealed beneath the eyes; the beak is three-jointed and covered 
at the base by the large labrum ; and the hemelytra are furnished with 
a distinct embolium. 

Although these are aquatic insects, they have been comparatively 
little modified for such a life. They carry air beneath their wings 
and obtain this air by pushing the tip of the abdomen 
above the surface of the water. 

They are predacious and are fond of reedy and 
grassy, quiet waters, where they creep about like the 
dytiscid beetles, creeping and swimming around and Fig. 422. — Pel- 
between the leaves and sprays of the submerged plants, ocorisfemor- 
seeking their prey. 

Only two genera of this family are represented in our fauna ; these 
are Pelocoris and Amhrysus. In Ambry sus the front margin of the 
prothorax is deeply excavated for the reception of the head; in 
Pelocoris this is not the case. 

Pelocoris. — Only three speciesof thisgenus are found in this country 
and these are restricted to the eastern half of the United States. 
The most common one is Pelocoris femordtus (Fig. 422). It measures 
about Q mm. in length, and when alive is more or less greenish testa- 
ceous in color; but after death it is pale yellow or brownish in color, 
with black or dark brown markings. 

Ambrysus. — Ten species of this genus have been found in this 
coimtry; they are restricted to the Far West. 



^ 



368 AN INTRODUCTION TO ENTOMOLOGY 

Family GELASTOCORID^ 

The Toad-shaped Bugs 

The Gelastocoridas was formerly known as the Galguhd«; conse- 
quently most of the references to these insects will be found under 
the older family name, which has been dropped, as the generic name 
Galgulus, on which it was based, is not tenable. 

In these insects the body is broad and short, and the eyes are 
prominent and projecting; the form of the body and the protuberant 
eyes remind one of a toad (Fig. 423). Ocelli are present. The an- 
tennae are short and nearly or quite concealed beneath the eyes. The 
beak is short, stout, and four-segmented. The fore legs are raptorial. 
The toad-shaped bugs live on the muddy margins 
of streams or other bodies of water. Some of them make 
holes for themselves, and live for a part of the time 
beneath the ground. They feed upon other insects, 
which they capture by leaping suddenly upon them. 
Their colors are protective and vary so as to agree with 
Fig-423 — G^^- the color of the soil on which they live. Hungerford 
Tatus!^^ °"^' ^3-S found that the eggs are buried' in the sand. Only 
five species are known to occur in this country. 
The most common and most widely distributed representative of 
the family found in this country is Gelasiocoris oculdtus (Fig. 423). 
Two other species of Gelastocoris are found in the Southern and 
Western States. In this genus the hemelytra are not fused and the 
fore tarsi are two-clawed. 

In the genus Mononyx, of which a single species, Mononyxfuscipes, 
is found in California, the hemelytra are free, but the fore tarsi are 
one-clawed. 

The genus Ncrthra is also represented in this country by a single 
species, Nerihra stygtea, which is found in Georgia and Florida. In 
this genus the hemelytra are fused together along a straight suture 
indicated by a groove. 

Family OCHTERID^ 

The Ochterids 

These are shore-inhabiting bugs, which are closely allied to the 
preceding family, in which they were formerly classed. They differ 
from the toad-shaped bugs in having the fore legs slender and fitted 
for running, and in having the short antenn£e exposed. They resemble 
the following family, the Saldidae, in having the beak long, reaching 
the hind coxs. The eyes are prominent, and two ocelli are present. 

The family includes a single genus, Ochterus, which, due to an 
error, has been commonly known as Pelogonus. Only three species 
occur in the United States; one of these was described from Virginia, 
one from Florida, and the third is widely distributed from the At- 
lantic Coast to Arizona. 



HEMIPTERA 3G9 

The widely distributed species is Ochterus americdnus . It measures 
5 mm. in length, and is blackish in color sprinkled with golden yellow 
points. On each side of the prothorax, behind the front angles, there 
is a bright yellow spot. 

The members of this family arc predacious. 



Family SALDID^E 
The Shore-Bugs 

With the Saldidag we reach the beginning of the extensive series 
of families of Hemiptera in which the antennse are prominent and 
are not concealed beneath the head. In this family the insects are of 
small size, and of dark colors with white or yellow markings. The 
head stands out free from the thorax on a cylindrical base. The an- 
tennse are four-jointed; there are two ocelli; the rostrum is three- 
jointed and very long, reaching to or beyond the middle 
coxae. The membrane of the wing-covers is furnished 
with looped veins, forming four or five long cells placed 
side by side. Occasionally there is little or no distinc- 
tion between the coriimi and the membrane. Two forms 
sometimes occur in the same species, one with a dis- 
tinct membrane, and another with the membrane thick- ^^2- 424- A 
ened and almost as coriaceous as the corium proper. ^ °'^^" ^^' 
The shape of these shore-bugs is shown by Figure 424. 

These insects abound in the vicinity of streams and other bodies 
of water, and upon damp soils, especially of marshes near our coasts. 
Some of the shore bugs dig burrows, and live for a part of the time 
beneath the ground. They take flight quickly when disturbed, but 
alight after flying a short distance, taking care also to slip quickly into 
the shade of some projecting tuft of grass or clod where the soil 
agrees with the color of their bodies. 

Thirty-three species belonging to this family have been found in 
the United States and Canada; these represent eight genera. 



m 



Family VELIID^ 

The Broad-shouldered Water-Striders 

The Velliidse includes insects which are very closely allied to the 
following family, the water-striders, both in structure and in habits. 
In both families the distal segment of the tarsi, at least of the fore 
tarsi, is more or less bifid, and the claws are inserted before the apex; 
these characters distinguish these two families from all other Hemip- 
tera. In the Veliidag the body is usually stout, oval, and broadest 
across the prothorax (Fig. 425). The beak is three-jointed; the legs 
are not extremely long, the hind femora not extending much beyond 




370 AN INTRODUCTION TO ENTOMOLOGY 

the end of the abdomen. In fact, the legs are fitted for running over 
the water, instead of for rowing, as with the Gerridje. The intermedi- 
ate legs are about equidistant from the front and hind pairs, except 
in Rhagovelia. These insects are dimor]3hic, both fully winged and 
short-winged or wingless adults occurring in the same species. 

About twenty species of this family have been found in America 
north of Mexico; these represent four genera. 

The broad-shouldered water-striders are found both on the banks 
of streams and ponds and on the surface of water. About one-half 
of our species belong to the genus Microvelia. These are very small, 
plump-bodied bugs, which are usually black and silvery in color or 
mottled with brown. They are found at the water's edge but run 
out on the water when disturbed ; and they are also often found upon 
rafts of floating vegetation. 

To the genus Rhagovelia belong somewhat larger forms, which are 
characterized by the long, deeply split, terminal 
segment of the tarsi of the middle legs. Our most 
common species of this genus is Rhagovelia obesa 
(Fig. 425). These bugs are found running over 
the surface of rapidly moving waters in streams. 
They can also dive and swim well under water. 
Four species of Rhagovelia are found in this p- . ^Rj^^^ovelia 
country-. _ ohesa. 

The genus Velia includes the larger members 
of the family. In these the tarsi of the middle legs are not cleft. 
Four species of this genus occur in our fauna. They are found on 
moderately rapid streams or little bogs and eddies connected there- 
with. 

The fourth genus occurring in our fauna is represented by a single 
species, Macrovelia harrhii, which is restricted to the Far West. 

Family GERRID.E 

The Water-Stnders 

This family includes elongated or oval insects which live upon the 
surface of water. Their legs are long and slender; the hind femora 
extend much beyond the apex of the abdomen ; the middle and hind 
pairs of legs are approximated and distant from the fore legs; the 
terminal segment of the tarsi, at least of the fore tarsi, is more or 
less bifid, and the claws are inserted before the apex. The beak is 
four-jointed. The antennae are long and four-jointed. 

The water-striders prefer quiet waters, upon which they rest or 
over which they skim rapidly; they often congregate in great 
nimibers. There are commonly two forms of adults belonging to the 
same species, the winged and the wingless; sometimes a third form 
occurs in which the adult has short wings. 

These insects are predacious; they feed on insects that fall into 
the water, and I have seen them jump from the water to capture flies 
and other insects that were flying near them. 



HEMIPTERA 371 

Twenty species of water-striders have been found in America 
north of Mexico; these represent seven genera. These genera are 
.separated by Hungerford ('19) as follows: 

A. Inner margin of the eyes sinuate behind the middle. Body comparatively 
long and narrow; abdomen long. (Subfamily Gerrinac). 
B. Pronotum sericeous, dull; antennae comparatively short and stout. 

C. First segment of the antennae shorter than the second and third taken 
together. 
D. Antennas half as long as the body; sixth abdominal segment of the 

male roundly emarginate Limnoporus 

DD. Antennae not half as long as the body, not extending beyond the 
thorax; sixth abdominal segment of the male doubly emarginate. 

Gerris 

CO. First segment of the antennae longer than the second and third taken 

together Gerris 

BB. Pronotum glabrous, shining; antennae long and slender. . .Tenagogonus 
AA. Inner margin of the eyes convexly rounded. Body comparatively short 
and broad ; abdomen so short as to appear almost nymphal in some forms. 
(Subfamily Halobatinae). 
B. First antennal segment much shorter than the other three taken together; 
not much longer than the second and third taken together, and some 
times shorter. 
C. Fourth (apical) segment of the antennas longer than the third. 
D. Eyes fairly prominent; colors of body black and yellow. .Trepobates 
DD. Eyes smaller, widely separated; body lead-colored, sericeous. 

ocean dwellers Halobates 

CO. Fourth segment of antennae never more than equal to the third; 
basal segm.ent of anterior tarsi much shorter than the second; 
hind femur equal to or much shorter than the hind tibia and tarsus 

taken together Rheumatobates 

BB. First antennal segment nearly equal to the remaining three taken to- 
gether, much longer than the second and third; antennae almost as 
long as the entire body; hind femur twice as long as hind tibia. 
Metrobates 

Gerris. — Of the twenty species of water-striders found in this 
country, nine belong to this genus; a common species in the East is 
Gerris conformis (Fig. 426). 




Fig. 426. — Gerris conformis. 

Limnoporus. — We have only a single species of this genus, L. ru- 
foscutilldhis. 

Tenagogonus. — Three species are listed from oiu* fauna, only one 
of which has been found in the North; this is T. gillettei, which is 
reported from Ohio. The others are found in Florida and California. 

Metrobates. — Our only species, M. hesperius, is found in Ontario 
and the eastern part of the United States. 



372 AN INTRODUCTION TO ENTOMOLOGY 

Trepobates. — This genus is represented only by T. pictus. This 
is a beautiful vellow and black species, which is quite widely distribut- 
ed. 

Rheumatobates.— Three species of this genus have been described. 
The males are remarkable for the strange form of the posterior femora, 
which are strongly bent, and the shape of the antennae, which are 
fitted for clasping. 

Halobates. — These are truly pelagic insects, living on the surface 
of the ocean, often hundreds of miles from land. They are most 
abundant in the region of calms near the equator; they feed on the 
juices of dead animals floating on the surface, and probably attach 
their eggs to floating sea-weed (Sargassum). H. micans is found off 
the coast of Florida and H. senceus off the coast of California. 

Family MESOVELIID^ 

The Mesoveliids 

This is a small family of which only two species have been found 
in North America. These are the following . 

Mesovelia mulsdnti. — This is a small bug, measuring only 4 or 
5 mm. in length; it is of a pale yellow color marked with brown. 
The antennae are long, filiform, and four-jointed; the beak is three- 
jointed; the legs are moderately long and slender; and the tarsi are 
three-jointed. This species is dimorphic, the adults being either winged 
or wingless. In the winged form, the membrane of the hemelytra is 
without veins. 

This species lives on the surface of quiet waters and on rafts of 
floating vegetation and is predacious. It is furnished with an ovi- 
positor and embeds its eggs in the stems of aquatic plants. 

Mesovelia douglasensis. — This is a smaller species than the pre- 
ceding; the length of the female is 2.1 mm., of the male 1.8 mm. It 
is olive-brown in color. It was recently discovered and described by 
Professor Hungerford ('24). It was found near Douglas Lake, Michi- 



Family HEBRIDiE 

The Hebrids 

This family includes very small plump-bodied bugs, measuring 
less than 3 mm. in length. The 
antennas are either four-jointed or five- 
jointed; the beak is three-jointed; and the 
tarsi are two-jointed. Ocelli are present. 
The head and thorax are sulcate beneath. 
The clavus of the hemelytra is similar in 
texture to the membrane, which is without 
^'uehru's ^^"'''^^'^'■°'' °^ veins (Fig. 427). Two genera of this family 
are found in the United States. 




HEMIPTERA 373 

Hebrus. — In this genus the antennas consist of five segments, not 
counting a minute segment at the base of the third. The 
adults are always winged. Four species occur in our fauna. These 
bugs are found on moist earth at the margins of pools and run out 
upon the water when disturbed; they are also found on floating 
vegetation. 

Merragdta. — In this genus the antennas are four-jointed not count- 
ing the small segment at the base of the third. The adults are dimor- 
phic, short-winged and long-winged forms occcurring in the same 
species. These insects inhabit still and stagnant waters and often 
descend beneath the surface; at such times the body is surrounded 
by a film of air. Only two species have been found, as yet, in this 
country. 

Family HYDROMETRID^ 

The Water-Measurers 

The members of this family are very slender insects, with linear 
legs andantennee (Fig. 428). The head is as long as the entire thorax, 
although this region is long also. The eyes are 
round, projecting, and placed a little nearer the 
base than the tip of the head. Ocelli are absent. 
The antennas are four-jointed; the beak is three- 
jointed; and the tarsi are three-jointed. 

These insects creep slowly upon the surface of 
the water; they carr>' the body considerably ele- 
vated, and are found mostly where plants are 
growing in quiet waters. It was probably their 
deliberate gait when walking on water that sug- 
gested the generic name Hydrometra, or water- 
measurer. In this country these insects have 
been commonly known under the generic name 
Limnobaies, or marsh-treaders ; but Hydrometra 
is much the older name. 

Only three species have been found in the 
United States. One of these, Hydrometra martini Fig. 428.— Hydrome- 
(Fig. 428), is widely distributed. The other two, ''« marfini. 
Hydrometra anstralis and Hydrometra wileyi, are 
found in the South. These insects are dimorphic both winged and 
wingless forms occurring in the same species. Descriptions of the 
three species are given by Hungerford ('23). 

The egg of Hydrometra martini is remarkable in form; it is figured 
on page 167. 

Family SCHIZOPTERID^ 

The Schizopterids 

This family and the following one, the Dipsocoridce, constitute a 
quite distinct superfamily, the members of which are most easily rec- 




374 



AN INTRODUCTION TO ENTOMOLOGY 



ognized by the form of the antennae (Fig. 429, h). These are four- 
iointed; the first two segments are short and thick; the third and 
for.rth segments are long, slender, and clothed with long hairs; 
the third segm.ent is thickened toward the base. In these two families 
ocelli are present; the beak is three- 
jointed; the legs are quite slender, and 
the tarsi are three-jointed. The species 
are small or very minute. 

The Schizopterid^ is distinguished 

from the following family by the shape 

of the head and the form of the cavities in 

which the front legs are inserted. The 

head when viewed from above is wider 

than long and is strongly deflexed; the 

fore coxal cavities are very prominent 

and timiidly formed. The beak is short. 

¥ig. ^2C).-GlvptocombHssaUator: The Schizopteridaj is represented in 

a, dorsal aspect ; b, antenna, our fauna by a single species, Glyptocom- 

(Aftcr Heidemann.) hus saltdtor (Fig. 429). This is a minute 

bug, measuring only 1.2 mm. in length 

and .6 mm. in width. The known specimens were taken on 

Plummers Island, Md. The describer of this species, Mr. O. 

Heidemann, states: "This species is most difficult to collect and is 

only to be found by sifting fallen leaves, rubbish and earth. The 

collector must watch patiently until the minute insect makes its 

presence known by jumping, and even then it takes a skillful hand 

to secure it in a vial." 




Family DIPSOCORID^ 
The Dipsocorids 

This family is closely allied to the preceding family; the dis- 
tinguishing features common to the two famiHes are indicated in the 
account of that family. 

In the Dipsocoridse the head is extended horizontally or slightly 
deflexed, and the fore coxal cavities are not at all prominent. The 
beak is long. 

This family is represented in our fauna by a single genus, Cera- 
tocombus, of which two or three species have been found in New 
Mexico; and one of these is doubtfully reported from Florida. These 
measure less than 2 mm. in length. 



Family ISOMETOPID.E 

The Isometopids 

This is a family of limited extent, there being very few species 
known in the entire world. It includes very small bugs, those found 
in this country ranging from 2 mm. to 2.6 mm. in length. 



HEMIPTERA 



375 



The Isometopldae is closely allied to the following family, the 
Mirid^; by some writers it has been classed as a subfamily of that 
family. In both families the antennae 
are four-jointed; the beak is four-jointed; 
the hemelytra are composed of clavus, 
coriimi, cuneus, and membrane; at the 
base of the membrane there are one or 
two cells; otherwise the membrane is with 
out veins. The Isometopidae is dis- 
tinguished from the following family by 
the presence of ocelli, two in number. 

Only four species of this family have 
been found in our fauna; one in Texas, 
one in Arizona, and two in the East. 
The Eastern species are Myiomma cixii- 
Jormis, which is dull black in color with a 
narrow white band across the base of the 
cuneus; and Isometopus pulchellns, which 
is easily recognizable by its contrasting 
colors of dark brown and yellowish white 
(Fig. 430). Both are exceedingly rare in- 
sects. 




Family MIRID^ 

The Leaf -Bugs 



Fig. 430. — Isometopus pulchel- 
lus. (After Heidemann.) 



This family, which has been known as the Capsidas, is more large- 
ly represented' in this country than any other family of the Hemiptera. 
Van Duzee in his "Catalogue of the Hemiptera North of Mexico" 
lists 398 species, which represent 129 genera. The species are usually 
of medium or small size. The form of the body varies greath^ in the 

different genera, which makes 
it difficult to characterize the 
family. 

The most available char- 
acter for distinguishing these 
insects is the structure of the 
hemelytra. These are almost 
always complete, and com- 
posed of clavus, corium, cuneus, 
and membrane. At the base of the membrane there are one or two 
cells; otherwise the membrane is without veins (Fig. 431). Other 
characters of the family are as follows: the ocelli are wanting; the 
beak and the antennae are each four-jointed ; the coxk are subelongate ; 
and the tarsi are three-jointed. 

It is impracticable to discuss here the divisions of this family; 

reference can be made to only a few of the more common species. 

The four-lined leaf-bug, Pcecilocdpsus linedtus. — This is a bright 




Fig. 431. — Hemelytron of Pcecilocapsus 
lineatus. 




370 AN INTRODUCTION TO ENTOMOLOCV 

yellow bug, marked with black. It measures about 8 mm. in length. 
There are four longitudinal black lines which extend over the 
prothoraxand the greater part of the hemeMra (Fig. 432). There is 
in many individuals a black dot on the cuneus of each hemelytron; 
and the membrane is also black. 

This insect infests various plants, but abounds most on the 
leaves of currant, gooseberry, mint, parsnip, Weigela, Dahlia, and 
rose. It punctures the young and tender leaves, causing small 
brown spots; but these are sometimes so numerous and closely 
placed that the leaves become completely withered. It is a widely 
distributed species, its range extending from Canada to Georgia and 
westward to the Rocky Mountains. 

There is only one generation a year. The eggs are laid in the 
terminal twigs of currant and other bushes in midsummer and hatch 
the following spring. They are laid in clusters, each 
containing six or eight eggs; these egg-clusters are 
forced out of the stem somewhat by the growth of the 
surrounding plant tissue; and as the projecting part of 
the egg is white, they can be easily found. 

The methods of control are the pruning and burning 
of twigs containing egg-clusters, and, early in the season . 
fu^^cal^su's ^^^ destruction of the nvTuphs by the use of kerosene 
lineatus. emulsion or some one of the tobacco extracts. 

The tarnished plant-bug, Lygus pratensis. — The 
tarnished plant-bug is a very common species which is found through- 
out the United States and in Canada. It is smaller than the preceding 
species, measuring 5 mm. in length and 2.5 mm. in its greatest width. 
It is exceedingly variable in color and markings ; its color varies from a 
dull dark-brown to a greenish or dirty yellowish brown. In the more 
typical forms the prothorax has a yellowish margin and several 
longitudinal yellowish lines; there i^ a V-shaped yellowish mark on 
the scutelltim ; the distal end of the corium is dark ; and the cuneus 
is pale, with a black point at the apex. 

This pest is a very general feeder; it has been recorded as injuring 
about fifty species of plants of economic value; its injuries to the 
buds of Aster, Dahlia, and Chr^^santhemum, and to the buds and 
blossoms of orchard-trees, and to nursery stock, are well-known. 
As yet no practical method of control of this pest has been foimd. 

The apple-redbug, Heterocordylus mdliniis. — This species and the 
following one are sometimes a serious pest in apple orchards. They 
cause spotting of the leaves; but, what is far more serious, they punc- 
ture the young fruit, which results either in the dropping of the 
fruit or in its becoming badly deformed so as to be unmarketable. 
The eggs are inserted into the bark of the smaller branches late in 
June or early in Jul}^; they hatch in the following spring soon after 
the opening of the leaves of the fruit-buds. The nymphs are tomato- 
red in color. They first attack the tender leaves, but as soon as the 
fruit sets they attack it. The young nymphs can be killed by an 



HEMIPTERA 377 

application of "black leaf 40" tobacco-extract diluted at the rate of 
I pint in 100 gallons of water; the efficiency of this spray is increased 
by the addition of about 4 pounds of soap to each 100 gallons. Two 
applications of the spray should be made: the first, just before the 
blossoms open; the second, just after the petals fall. The spraying 
should be done on bright warm days, for in cool weather many of the 
n^TTLphs hide away in the opening leaves. 

The adult apple-redbug is about 6 mm. long. The general color 
varies from red to nearly black. Usually the thorax is black in front 
and red behind. The wings are red, usually black along the inner 
edge and with a pointed ovate black spot near the outer margin. 
The scutellimi, legs, and antenna are black. The entire dorsal sur- 
face is sparsely covered with conspicuous white, flattened, scale-like 
hairs. 

The false apple-redbug, Lygideamendax.- — -This species resembles 
the preceding one in general appearance and in habits. The nymphs 
can be distinguished by their brighter red color, by the absence of 
dusky markings on the thorax, and by having the body clothed with 
fine, short, black hairs. The adult of this species is lighter-colored and 
lacks the scale-like hairs on the dorsal surface. 

The above account of these two species is an abstract of one pub- 
lished by Professor C. R. Crosby ('11). 

The hop-redbug, Paracalocoris hawleyi.— The leaves of hop plants 
are sometimes perforated and the stems stunted and deformed by the 
nymphs of this species, which are red with white markings. The 
adult is 6 mm. long, black, with hemehi:ra hyaline or pale yellowish, 
and the cuneus reddish. For a detailed account see Hawley ('17). 

Family TERMATOPHYLID^ 

The Termatophylids 

This family is closely allied to the following one, the Anthocoridse, 
but differs in that the beak is four-jointed and ocelli are wanting. 
The hemelytra are well developed, furnished with an embolium, and 
usually with a single large cell in the membrane. The tarsi are three- 
jointed and are not furnished with an aroliimi. 

The Termatophylidas is a very small family, but it is world-wide 
in its distribution. A single ver\' rare species has been found in this 
country. This is Hesperophylum heidemanni, which has been taken 
in New Hampshire and Arizona. Only the female of this species has 
been described. It is dark brown with the scutellum yellowish white; 
the cell in the membrane of the hemelytra is semicircular; the length 
of the body is 4 mm. 

Family ANTHOCORIDSE 

The Flower-Bugs 

This family is closely allied to the following one; but in the 
flower-bugs ocelli are present, though sometimes difficult to see, 




378 AN INTRODUCTION TO ENTOMOLOGY 

and the hemelytra are almost always fully developed and are furnished 

with an emboliirm (Fig. 433). As in the following family, the beak 

consists of three segments; the 
antennse, of four; and the tarsi, 
of three. 

The species are small. They 
are found in a great variety of 
situations, often upon trees and 
on flowers, sometimes under bark 
or rubbish. They are predacious. 
Fig- 433.— Hemelytron of Triphelps. Thirty-six species have been 

catalogued in our fauna; these 

represent thirteen genera. The following species will serve as an 

example. 

The insidious flower-bug, Triphelps insidiosus. — This is perhaps 
the best-known of our species. It is a small black bug, measuring 
only 2 mm. in length; the hemelytra are yellowish white on the 
corium, at the tip of which is a large, triangular, blackish spot; the 
membrane is milky white. This species is widely distributed; it is 
common on flowers, and is often found preying upon the leaf -inhabit- 
ing form of the grape Phylloxera; it is also often found in company 
with the chinch-bug, upon which it preys and for which it is some- 
times mistaken. 

Family CIMICIT>M 

The Bedbug Family 

The members of this family are parasitic bugs, which are either 
wingless or possess only vestigial hemelytra. In these insects the 
ocelli are absent, the antennce are four-jointed, the beak is three- 
jointed, and the tarsi are three-jointed. Only four species belonging 
to this family have been found in America north of Mexico. These 
can be separated by the following table, which is based on a more 
detailed one given by Riley and Johannsen ('15). 

A. Beak short, reaching to about the anterior coxae. 

B. Pronotum with the anterior margin very deeply sinuate. The genus Ctmex. 
C. Body covered with very short hairs; second segment of the antennae 
shorter than the third; hemelytra with the inner margin rounded and 
shorter than the scutellum. The common bedbug. . .C. led uldrius 
CC. Body covered with longer hairs; second and third segments of the an- 
tennae of equal length; hemelytra with the inner margin straight 
and longer than the scutellum. Species found on bats. . .C.pilosellus 
BB. Anterior margin of the pronotum very slightly sinuate or nearly straight 
in the middle. Species found in swallows' nest?,. . .CEclacus vicar ius 
AA. Beak long, reaching to the posterior coxae. Infests poultry in southwest 
United States and in Mexico Hcematosiphon inodorus 

The common bedbug, Clmex lectuldrius. — The body is ovate in 
outline and is very flat (Fig. 434) ; it is reddish brown in color, and is 
4-5 mm. long by 3 mm. broad when full-grown. This pest is a noc- 



IJEMIPTERA 



379 



Fig.434.— Cfwex 
lectularius. 



tumal insect, hiding by day in cracks of furniture and beneath various 
objects. Ordinarily it is found only in the dwellings of man; but it 
has been known to infest chicken houses. The means 
commonly employed to destroy this pest is to wet 
~^^^ the cracks of the bedstead and other places in which 

T ^"Pffl«^ ^^ hides with corrosive sublimate dissolved in alco- 
f^^'x" ^*-*^' '^^^^ ^^ ^^^"^ ^^' druggists under the name of 
/^^\ bedbug poison. As this substance is a virulent 

poison, it should be used with great care. In case a 
room is badly infested, it should be thoroughly 
cleaned; fumigated with sulphur or with hydro- 
cyanic acid gas; the walls repapered, kalsomined, 
or whitewashed ; and the woodwork repainted. Detailed directions 
for the use ot gases against household insects are given by Herrick 
{'14). In traveling, where one 
is forced to lodge at places in- 
fested by this insect or by fleas, 
protection from them can be had 
by sprinkling a small quantity 
of pyrethrum powder between 
the sheets of the bed on retiring. 
The other members of this 
family found in this country can 
be distinguished from the com- 
mon bedbug b}' means of the table 
given above. 

Family POLYCTENID^ 



The Many-combed Bugs 

The Polyctenidas includes a 
small number of very rare species 
of bugs that are parasitic upon 
bats. Until recently it was not 
known to be represented in 
America north of Mexico; but 
Ferris ('19) records the finding 
of one species, Hesperoctenes longi- 
ceps, on the bat Eumops calif orni- 
ctis, near San Bernardino, Cali- 
fornia. Figure 435 is a reduced 
copy of a figure of this insect by 
Ferris. The left half of the figure 
represents the dorsal aspect of 
this insect; the right half, the 
ventral aspect. This carefully made figure renders a detailed 
description unnecessary. The length of the body of the female is 4.5 
mm.; of the male, 3.8 mm. 




rig. 435. — Hesperoctenes longiceps: A, 
female, left half dorsal, right half ven- 
tral; B, posterior tarsus; C, anterior 
tarsus; D, dorsal aspect of second an- 
tennal segment, distal end upward. 
(After Ferris.) 




ScSn AN INTRODUCTION TO ENTOMOLOGY 

In this family the hemelytra are vestigial and the hind and middle 
tarsi are four-jointed. The name of the typical genus, Polyctenes, was 
probably suggested by the presence of several comb-like series of 
spines on the body. 

Family NABID^ 
The Nabids 

In this family the body is oblong and somewhat oval behind. 
The beak is long, slender, and four-jointed. The hemelytra are 

longer than the abdomen, or are 
very short. Some species are di- 
morphic, being represented by 
both long-winged and short-wing- 
ed forms. In the forms with long 
wings the membrane is usually 
furnished with four long veins 
-Hemelytron of Nahs ferns, bo^^ding three discal cells, which 
are often open; from these discal 
cells diverge veins which form several marginal cells (Fig. 436). 
The fore tibi^ are armed with spines and are capable of being closed 
tightly upon the femora, which are stout; they are thus fitted for 
grasping prey. 

Nearly all of our common species belong to the genus Nobis; in 
fact this genus includes twenty-six of the thirty-one species found in 
this country. Due to an error made long ago, this genus has been 
commonly known as Corhcus; and most of the references to these 
insects are under this name. 

Nobis ferus: — This is one of our most common species. It measures 
about 8 mm. in length. It is pale yellow with numerous minute 
brown dots; the veins of the membrane are also brownish. This 
species is distributed from the Atlantic Coast to the 
Pacific. It secretes itself in the flowers or among the 
foliage of various herbaceous plants, and captures small 
insects upon which it feeds. 

Nobis subcoleopirdtus. — The short-winged form of 
this species is another very common insect (Fig. 437). 
This is of a shining jet-black color, with the edge of 
the abdomen and legs yellowish. The hemelytra 
barely extend to the second abdominal segment. The 
long-winged form of this species is not common; it is 
much narrower behind, and the hemel>i;ra and the ab- 
domen are rather dusky , or piceous, instead of jet-black. 

Family REDUVIID^ 
The Assassin-Bugs 

The Reduviida2 is a large family, including numerous genera of 
diverse forms. Many of the members of it are insects of considerable 




HEMIPTERA 



381 



size, and some are gayly colored. They are predacious, living on the 
blood of insects. In some cases they attack the higher animals; and, 
occasionally, even man suffers from them. 




Fig. 438. — Arilus cristatus. (From Glover.) 



In this family the beak is short, three-jointed, attached to the 
tip of the head, and with the distal end, when not in use, resting upon 
the prostemimi, which is grooved to receive it. Except in a few spe_ 
cies, ocelli are present in the winged forms. The anten- 
HcB are four-jointed. 

More than one hundred species occur in our fauna ; 
these represent forty-four genera. The following species 
will serve to illustrate the great diversity in form of 
members of this family. 

The wheel-bug, Arilus cristatus. — The wheel-bug is 
so called on account of the cogwheel-like crest on the 
prothorax (Fig. 438). It is a common insect south of 
New York City, and is found as far west as Texas and 
New Mexico. The adult, a cluster of eggs, and several 
n>Tnphs, are represented in the figure. The nymphs 
when young are blood-red, with black marks. 

The masked bedbug-hunter, Reduvius persondtus. — The adult of 
this species is represented by Figure 439; it measures from 15 to 20 
mm. in length, and is black or very dark brown in colo- 




382 A N I NT ROD UCTION TO ENTOMOLOG Y 

There are two marked peculiarities of this species that have caused 
it to attract much attention : first, in its immature instars the body 
is covered with a viscid substance which causes particles of dust and 
fibers to adhere to it ; not only the body, but the legs and antenna 
also, are masked in this way; in fact the nymph resembles a mass of 
lint, and attracts attention only when it moves; second, this species 
infests houses for the sake of preying upon the bedbug. It feeds also 
upon flies and other insects. 

The big bedbug, Tridtoma sanguisuga. — Closely allied to the 
masked bedbug-hunter is a large bug which insinuates itself into beds 
for a less commendable purpose than that of its ally, for it seeks 
human blood at first hand. This insect measures 25 mm. in length; 
it is black marked with red; there are six red spots on each side of 
the abdomen, both above and below. It inflicts a most painful wound. 
This is one of several species of the Reduviidse that received the 
name of "kissing-bug" as a result of sensational newspaper accounts 
which were widely published in the summer of 1899 and which stated 
that a new and deadly bug had made its appearance, which had the 
habit of choosing the lips or cheeks for its point of attack on man. 
It is found from New Jersey south to Florida and west to Illinois 
and Texas. 

The genus Triatoma was renamed Conbrhimis and most of the 
references to this species are under this generic name. 

The thread-legged bug, Eniesa brevipennis. — This is our most 

common representative cf one 
of the subfamilies of the Redu- 
viidffi in which the body is slen- 
der and the middle and hind 
legs are thread-like (Fig. 440). 
The front legs are less thread- 
like, and are fitted for grasp- 
ing ; they suggest by their form 
the front legs of the Mantidae; 
the coxa is greatly elongated, 
more than four times as long as 
-Emesa brevipennis. thick; the femur is spined; 

and the tibia shuts back upon 
the femur. In Figure 440 they are represented beneath the thread- 
like antennae. Emesa brevipennis measures about 33 mm. in length; 
it is found upon trees, or sometimes swinging by its long legs from the 
roofs of sheds or barns. 

A monograph of the Reduviidc^ of North America has been 
published by Fracker ('12). 

Family PHYMATID^ 
The Ambush-Bugs 

The Phymatidse is poorly represented in this country but some of 
the species are very common. Here we find the body extended 




HEMIPTERA 



383 



w^ 



Fig. 44I- — 
Phymata er- 
osa. 



laterally into angular or rounded projections, suggesting the name 
of the "typical genus. But the most striking character which dis- 
tinguishes this group is the remarkable form of the front legs. These 
are fitted for seizing prey. The coxa is somewhat elongated ; the femur 
is greatly thickened, so that it is half or two thirds as broad as long; 
the tibia is sickle-shaped, and fits closely upon the broadened and 
curved end of the femur; both tibia and femur are armed with a 
series of close-set teeth, so that the unlucky insect that is grasped 
by this organ is firmly held between two saws; the apparently useless 
tarsus is bent back into a groove in the tibia. Another striking 
character is presented by the antennas, the terminal 
segment being more or less enlarged into a knob. 
Under the lateral margin of the pronotum in Phymata 
there is on each side a groove into which the antenna 
fits. 

Only two genera are represented in our fauna, each 
by six species. These are Phymata and Macrocephalus. 
In Phymata the scutellimi is of ordinary size; in Macro- 
cephalus it is very large and extends to the tip of the abdomen. 
Our most common species is Phymata erosa (Fig. 441). It is a 
yellow insect, greenish when fresh, marked with 
a broad black band across the expanded part of 
the abdomen. It conceals itself in the flowers 
of various plants, and captures the insects which 
come to sip nectar. It is remarkable what large 
insects it can overcome and destroy; cabbage 
butterflies, honey-bees, and large wasps are over- 
powered by it. 

Family ENICOCEPHALID^ 

The Unique-headed Bugs 

In this family the hemelytra are wholly mem- 
branous and provided with longitudinal veins 
and a few cross-veins (Fig. 442). The head is 
constricted at its base and behind the eyes, and is 
swollen between these two constrictions. This 
is a form of head not found in any other Hemip- 
tera. Ocelli are present. The antennce are four- 
jointed; the first, second, and third segments are 
each followed by a small ring-joint. The beak is 
four-jointed. The front tarsi are one-jointed, the middle and hind 
tarsi two-jointed. The front legs are fitted for grasping prey, the 
fore tarsi being capable of closing upon the end of the broad tibiae.^ 

This is a small family ; but few species are known from the entire 
world, and only two have been described from America north of 
Mexico. These are Enicocephalus formicina, found in California, 
and Systelloderus bleeps, which has been found from New York to Utah. 




Fig. 442. — Systello - 
derus biceps. (Af- 
ter Johannsen.) 



3S4 AN INTRODUCTION TO ENTOMOLOGY 

But little has been published regarding the habits of these insects. 
It is evident, from the structure of their fore legs, that they are 
predacious. Professor Johannsen ('09 b) found Systelloderus biceps 
{Henicocephalus culicis) flying in small swarms near Ithaca, N. Y. 
Their manner of flight resembled that of chironomids. They were 
observed repeatedly from July 5 to the last week in August, always in 
the latter part of the afternoon. This species measures 4 mm. in 
length. 

The type genus of this family was first named Enicocephalus ; this 
name was later emended to Henicocephalus ; but the older form of the 
name, though incorrectly formed, is now used. 

Family TINGID.E 

The Lace-Bugs 

The Tingida? are doubtless the most easily recognized of all Hemip- 
tera. The reticulated and gauze-like structure of the hemelytra, 
usually accompanied by expansions of the pro- 
thorax of a similar form, gives these insects a 
characteristic appearance which needs only to 
be once seen to be recognized in the future. 
Figure 443 represents one of these insects 
greatly enlarged, the hair-line at the side 
indicating the natural size of the insect. They 
are generally very small insects. But they 
occur in great numbers on the leaves of trees 
and shrubs, which they puncture in order to 
suck their nourishment from them. 

In this family the ocelli are wanting; the 

beak and antennse are four-jointed; the scu- 

Fig- A\2>-—Corythucha tellimi is usually wanting or vestigial, replaced 

"''""^'^- by the angular hind portions of the pronotum; 

and the tarsi are tw^o-jointed. 
About seventy-five species of lace-bugs, representing twenty-three 
genera, are now listed from this country. There are two well-marked 
subfamilies. 

Subfamily TINGING 

This division includes nearly all of the known species. Here 
the scutellum is usually covered by an angular projection of the 
pronotum ; and the hemelytra have no distinction between the clavus, 
corium, and membrane. The following species will serve as an il- 
lustration of this subfamily. 

' _ The hawthorn lace-bug, Corythucha arcudta. — This is a widely 
distributed species, which punctures the under surface of the leaves 
of different species of Cratcegus. The infested leaves have a brown 
and sunburnt appearance. Eggs, nymphs, and adults are found 
together. The adult is represented, much enlarged, in Figure 443. 




HEMIPTERA 



385 



In Figure 444 the eggs and a nymph are shown. The eggs are covered 
uy a brown substance, which hardens soon after oviposition. 

Subfamily PIESMIN.E 

In this subfamily the scutellum is not covered; the hemelytra 
have a distinct clavus, with a well-marked claval suture; the clavus 
is furnished with one, and the coriimi with three, 
longitudinal veins which are much stronger than 
the network of veins between them. In long- 
winged individuals the tip of the membrane lacks 
the network of veins and appears like the mem- 
brane in other families. As yet but a single 
American species has been described. 

The ash-gray Piesma, Piesma cinerea. — This 
species measures about 3 mm. in length, and is of 
an ash-gray color. The prothorax is deeply pitted, 
so that it presents the same appearance as the 
base of the wing-covers. The head is deeply 
bifid at tip, and there is a short robust spine be- 
tween the eye and the antenna on each side. This 
species sometimes infests vineyards to an injurious 
extent, destroying the fiower-buds in early spring. 

Family PYRRHOCORID^ 




Fig. 444.— Eggs and 
nymph of Cory- 
thucha arcuata. 




The Cotton-Stainer Family 

In this family the antennae are four-jointed; the beak is also 
four-jointed; ocelli are absent ; and the hemelytra are not furnished 

with a cuneus. The members of 
the family are stout and heavily 
built insects, and are generally 
rather large and marked with 
strongly contrasting colors, in 
which red and black play a con- 
spicuous part, in this respect re- 
sembling some of the larger 
species of the following family. 
The Pyrrhocoridee can be dis- 
tinguished from the Lygaeidas by the absence of ocelli, and by the 
venation of the membrane of the hemelytra (Fig. 445). At the base 
of the membrane there are two or three large cells, and from these 
arise branching veins. 

Only twenty-two species, representing five genera, have been found 
in our fauna, and these are restricted to the Southern and Western 
States. 

Our most important species, from an economic standpoint, is the 
red-bug or cotton-stainer, Dysdercus suturellus (Fig. 446). It is 



Fig. 445. — Hemelytron of Euryopthal 
mus succinctiis. 



386 



AN INTRODUCTION TO ENTOMOLOGY 



oblong-oval in form, of a red color; the hemelytra and an arc on 
the base of the prothorax, and also the scutelltim, are pale brown. 
The hemel>i:ra have the costal margin, a narrow line bordering the 
base of the membrane and continuing diagonally along the outer 
margin of the clavus, and also a slender streak on the inner margin of 
the clavus, pale yellow. It varies much in size, ranging from _io mm. 
to 1 6 mm. in length. The young bugs are bright red 
with black legs and antennas. From time immemorial 
this has been one of the worst pests with which the 
cotton-planters of Florida and the West Indies have 
had to contend. It does much damage by piercing 
the stems and bolls with its beak and sucking the sap ; 
but the principal injury to the crop is from staining 
the cotton in the opening boll by its excrement. It 
is also injurious to oranges ; it punctures the rind of 
the fruit with its beak; and soon decay sets in, and 
the fruit drops. These insects can be trapped in 
cotton-flelds by laying chips of sugar-cane upon the 
earth near the plants ; in orange-groves small heaps 
of cotton-seed will be found useful, as well as pieces of sugar-cane. 
The insects that collect upon these traps can be destroyed with hot 
water . 

The species whose range extends farthest north is Euryophthdlntus 
succinctus. This is found from New Jersey south to Florida and 
west to Arizona. It is brownish black, with the lateral and 




Fig. 446.- — Dys- 
dercus suturelliis 



hind margins of the prothorax, 
elytra, and the edge of the 
abdomen, margined with orange 
or red. It measures about 15 
mm. in length. 

Family LYG^ID^ 

The Chinch-Bug Family 



the costal margin of the hem- 




Fig. 447. — Hemelytron of Lygaus 
kalmii. 



The Lygseidas is one of the larger families of the Hemiptera. It 
includes certain forms which closely resemble members of the pre- 
ceding family in size, form, and strongly contrasting colors. But the 
great majority of the species are of smaller size and less brightly col- 
ored ; and all differ from that family in presenting distinct ocelli. The 
membrane of the hemelytra is furnished with four or five simple veins, 
which arise from the base of the membrane ; sometimes the two inner 
veins are joined to a cell near the base (Fig. 447). 

Nearly two hundred species belonging to this family have been 
found in our fauna; these represent fifty-five genera and seven 
subfamilies. Although these insects feed on vegetation, they have 
attracted but little attention as pests of cultivated plants excepting 
the following species. 




HEMIPTERA 387 

The chinch-bug, Bltssus leiicopterus. — This well-known pest of 
grain-fields is a small bug, which when fully grown measures a little 
less than 4 rrjn. in length. It is blackish in color, with conspicuous, 
snowy white hemel\ tra. There is on the costal margin of each 
hemeh'tron near the middle of its length a black spot ; from each of 
these spots there extends towards the head a some- 
what Y-shaped dusky line. The body is clothed 
with numerous microscopic hairs. In Figure 448 
this insect is represented natural size and enlarged. 
The species is dimorphic, there being a short-winged 
form. 

There are two generations of the chinch-bug each p^g ^^^,—Blissus 
year. The insects winter in the adult state, hiding leucoptems. 
beneath rubbish of any kind; they even penetrate 
forests and creep under leaves, and into crevices in bark. In early 
spring they emerge from their winter quarters and pair; soon after, 
the females begin to lay eggs; this they do leisurely, the process being 
carried on for two or three weeks. The eggs are yellowish ; about 500 
are laid by a single insect; they are deposited in fields of grain, be- 
neath the ground upon the roots, or on the stem near the surface. 
The eggs hatch in about two weeks after being laid. The newly 
hatched bugs are red; they feed at first on the roots of the plant 
which they infest, sucking the juices; afterw^ards they attack the 
stalks. The bugs become full-grown in from forty to fifty days. 
Before the females of this brood deposit their eggs, they leave their 
original quarters and migrate in search of a more abundant supply 
of food. About this time the wheat becomes dry and hard; and the 
migration appears to be a very general one. Although the insects 
sometimes go in different directions, as a general rule the masses 
take one direction, which is towards the nearest field of oats, corn, or 
some other cereal or grass that is still in a succulent state. At this 
time many of the bugs have not reached the adult state ; and even in 
the case of the fully winged individuals the migration is usually on 
foot. In their new quarters the bugs lay the eggs for the second or 
fall brood. 

The methods of control of this pest that are used are the fol- 
lowing : the burning in autumn of all rubbish about fields, in fence 
comers, and in other places where the bugs have congregated to 
pass the winter; the stopping of the marching of the spring brood 
into new fields by means of a furrow or ditch with vertical sides, and 
with holes like post -holes at intervals of a few rods in the bottom of 
the furrow or ditch, in which the bugs are trapped; the use of a 
line of gas-tar on the ground to stop the marching of the spring 
brood ; in some cases kerosene emulsion has been used to advantage ; 
the sowing of decoy plots of attractive grains in early spring, and the 
later plowing under of the bugs and their food and harrowing and 
rolling the ground to keep the bugs from escaping; and the artificial 
dissemination of the fungus Sporotrichum globuliferum, which is the 
cause of a contagious disease of the chinch-bug. 



388 AN INTRODUCTION TO ENTOMOLOGY 

Family NEIDID^ 

The Stilt-Bugs 

The family Neididse consists of a small number of species, which 
on account of their attenuated forms are very striking in appearance 
(Fig. 449). The body is long and narrow; 
the legs and antennae are also long and 
extremely slender. There is a transverse 
incision in the vertex in front of the ocelli. 
The antennae are four-jointed, elbowed at 
the base of the second segment, and with 

f/\\x/A the tip of the first segment enlarged. The 

y \X/ \_ beak is four-jointed; and the membrane 

r JT ^ r of the hemelytra is furnished with a very 
I /H\ \ few veins, 

r* / H \ ^ -i Only eight species of this family have 

been found in our fauna; but these repre- 
sent six genera. Only two of the species 
are widely distributed in the United 
States and Canada. These are sluggish 
insects, found in the undergrowth of 
woods and in meadows and pastures. 
Jalysus spindsus. — This is the best- 
known member of this family. It is distributed from the Atlantic to 
the Pacific in both the United States and Canada. It is as slender as a 
crane-fly (Fig. 449) and of a pale tawny color. The front of the head 
tapers off to an almost acute, upturned point. An erect spine projects 
from the base of the scutellum, and another from each side of the 
mesopleura, just in front of the posterior coxas. The body is about 
8 mm. in length. 

Jalysus perclavdtus. — This is one of the southern members of the 
family, but it has been found in New Jersey and the District of 
Columbia. It is smaller than the preceding species; the length of 
the male is 5 mm., of the female 6 mm. There is an erect spine be- 
tween the bases of the antennas; and the last segment of the antennae 
is shorter and thicker than in J. spinosus. 

Neides miiticus .—L^ke Jalysus spinosus, this species is found from 
the Atlantic to the Pacific in both the United States and Canada. 
It lacks the spines of the scutellum and thorax; and the front of the 
head is bent down, in the form of a little horn. 

The other representatives of this family in our fauna are found in 
Florida, Arizona, New Mexico, and California. 




Fig. 449. — Jalysus spinosus. 



Family ARADIDiE 

The Flat-Bugs 

The members of this family are very flat insects; in fact they 
are the flattest of all Hemiotera. The-/ live in the cracks or beneath 



HEMIPTERA 



389 



the bark of decaying trees; and the form of the body is especially 
adapted for gliding about in these cramped situations. They are 
usually dull brown or black ; sometimes they are varied with reddish 
or pale markings. The hemelytra are usually well 
developed, with distinct corium, clavus, and mem- 
brane; but they are reduced in size, so that when 
folded they cover only the disk of the abdomen (Fig. 
450). Ocelli are lacking; the antennas are four-jointed ; 
the tarsi are two-jointed; and the beak is four-jointed, 
but often apparently three-jointed. 

These insects are supposed to feed upon fungi or 
upon the juices of decaying wood and bark. The 
family is well represented in this country; fifty-nine species, repre- 
senting nine genera, are now known, and doubtless many remain to 
be discovered. 



* 



Fig. 450.— ^r- 
adiis acutus. 




Fig. 451. — Hemely 
trivittattis. 



Leptocoris 



Family COREID^ 
The Squash-Bug Family 

The members of this family vary greatly in form. Some of the 
species are among the most formidable in appearance of all of our 
Hem.iptera ; while others are comparatively weak and inconspicuous. 

The family is characterized as 
follows : the antenna are insert- 
ed above an ideal line extending 
from the eye to the base of the 
rostrum, and are four-jointed ; 
the vertex is not transversely im- 
pressed; the ocelli are present; 
the beak is four-jointed; the 
scutellum is small or of mediiim 
size; the hemelytra are usually complete and composed of clavus, 
coriiim, and membrane; the membi ane is furnished with many veins, 
which spring from a transverse basal vein, and are usually forked 
(Fig. 451); the tarsi are three-jointed. 

This is a large family ; one hundred and twenty- 
four species, representing forty-eight genera, have 
been found in our fauna. It contains both vegetable 
feeders and carnivorous forms ; in some cases the same 
species will feed upon both insects and plants. The 
most common and best-known species is the following. 
The squash-bug, Anzsa trhtis. — The form of the 
body of the adult insect is represented in Figure 452. 
In this stage the insect appears blackish brown above 
and dirty yellow beneath. The ground color is really 
ochre-yellow, darkened by numerous minute black 
punctures. Upon the head are two longitudinal 
black stripes; the lateral margins of the prothorax 
ars } ellow, owing to the absence of the punctures along a narrow 




Fig. 45 2. — Anasa 
Irislis. 



390 



AN INTRODUCTION TO ENTOMOLOGY 



space; and the margin of the abdomen is spotted with yellow from. 

a similar cause; the membrane of the hemelytra is black. 

This species winters in the adult state. 
In early simmier it lays its eggs in little 
patches on the young leaves of squash and 
allied plants. The young bugs are short 
and more rounded than the adult insects. 
There are several generations of this 

/^•^mt^m^'**^ species each year. 

J^^^^^^ This is one of the most annoying of 

JJ^i/W^ \^ the many pests of the kitchen-garden; 
.J^im^m ^ and, unfortunately, no satisfactory meth- 
od of control has been devised. The egg 
masses are conspicuous and can be col- 
lected and destroyed ; the young nymphs 
can be killed by spraying with io% 
kerosene emulsion; the adults can be 
trapped under bits of boards and stones; 
and many nymphs can be killed by de- 
stroying "the vines as soon as the crop is 
harvested. 

Acanthocephala femordta (Fig. 453) will serve as an example of 
one of the larger members of this family. This species is distribut- 
ed from North Carolina to Florida and Texas. It has been known 
to destroy the cotton-worm, and is said to injure the fruit of the 
cherry by puncturing it with its beak and sucking the juices. 




Fig. 453. — Acanthocephala 
femorata. (From Glover.) 



Family PENTATOMID^ 



The Stink-Bug Family 



With the Pentatomidas we reach a series of families, three in 
number, in which the antennas are usually five-jointed, differing in 
this respect from all of the preceding families. _ The 
form of the body presented by the great majority of 
the members of the Pentatomidse is well shown by 
Figure 454. It is broad, short, and but slightly convex; 
the head and prothorax form a triangle. The scutellum 
is narrowed behind ; it is large and in a few forms nearly 
covers the abdomen. The tibias are unarmed or are 
furnished with very fine short spines. 

As with the Coreidae, the members of this family Fig. 454.— A 
varv^ greatly in their habits; some are injurious to pentatomid. 
vegetation; others are predacious; while some species 
feed indifferently upon animal or vegetable matter. vSome species 
are often found on berries and have received the popular name of 




HEMIPTERA 391 

stink-hugs on account of their fetid odor, which they are apt to 
impart to the berries over which they crawl. This nauseous odor is 
caused by a fluid which is excreted through two openings, one on 
each side of the lower side of the body near the middle coxae. 

The harleqtiin cabbage-bug, Murgdntia histrionica. — Among the 
species of the Pentatomidas that feed upon cultivated plants, the 
harlequin cabbage-bug or "calico-back" is the most important pest. 
It is very destructive to cabbage and other cruciferous plants in the 
vSouthern States and on the Pacific Coast. It is black, with bands, 
stripes, and margins of red or orange or yellow. Its bizarre coloring 
has suggested the popular names given above. The full-grown bugs 
live through the winter, and in the early spring each female lays on 
the under surface of the young leaves of its food-plants about twelve 
eggs in two parallel rows. The eggs are barrel-shaped and are white 
banded with black. The young bugs are pale green with black spots. 
They mature rapidly; and it is said that there are several generations 
in one season. 

This is an exceedingly difficult species to contend against. Much 
can be done by cleaning up the cabbage stalks and other 
remnants as soon as the crop is harvested, and, in the 
following spring, trapping the bugs that have hiber- 
nated by placing turnip or cabbage leaves in the in- 
fested gardens or fields, or by planting trap-crops of 
mustard or other cruciferous plants. The bugs that 
are not collected by these methods and their eggs 
should be collected by hand; this can be easily done Fig. 455.- P«(/- 
as both the bugs and their eggs are conspicuous. "''^^ . ^y"l^- 

As if to atone for the destruction caused by their Gfover.) 
relative, the harlequin cabbage-bug, there are many 
members of this family that aid the agriculturist by destroying 
noxious insects. The species of the genus Podisus have been reported 
often as destroying the Colorado potato-beetle, currant worms, and 
other well-known pests. Figure 455 represents a member of this 
genus, Podisus niactiliventris 

Family CYDNID^ 
The Bnrrower-Biigs and the Negro-Bugs 

The Cydnidfe is the second of the series of families in which the 
antennae are five-jointed. In this family the outline of the body is 
more generally oval, rounded, or elliptical, and the form more convex, 
than in the Pentatomidae. The scutellum is large but varies greatly 
in size and in outline. Each lateral margin of the scutellum is fur- 
nished with a furrow into which the margin of the hemelytron of 
that side fits. In this respect the Cydnidas agrees with the preceding 
family and differs from the following one. The tibiae are armed with 
strong spines. 

The family includes two well-marked subfamilies. 





392 AN INTRODUCTION TO ENTOMOLOGY 

Subfamily CYDNIN^ 

The Burrower-Bugs 

The subfamily Cydninaa includes the greater niunber of the mem- 
bers of the Cydnidag found in the United States and Canada ; of these 
there are twenty-nine species now listed, representing 
nine genera ; most of these are restricted to the South 
and the Far West. 

In this subfamily the scutellum is either broad 

and bluntly rounded, or triangular with the apex 

pressed down. The species are generally black or 

very dark brown. They are found burrowing in 

sandy places, or on the surface of the ground beneath 

sticks and stones, or at the roots of grass and other 

herbage. A European species is said to suck the sap 

from various plants near the ground. It is desirable 

that further observations be made upon the habits of this subfamily. 

Figure 456 represents Cyrtomenus mirabilis, a species found in the 

South and the Southwest. 



Subfamily THYREOCORIN^ 
The Negro-Bugs 

The subfamily Thyreocorinaj is represented in our fauna by a 
single genus, Thyreocoris, of which sixteen species have been found 
in this country. They are mostly black and beetle-like 
in appearance, some have a bluish or greenish tinge, 
and all are very convex. The body is short, broad, 
and very convex, in fact almost hemispherical. The 
scutellum is very convex and covers nearly the whole 
of the abdomen. 

These insects infest various plants, and often in- 
jure raspberries and other fruits by imparting a dis- 
agreeable, bedbug-lilce odor to them. A common and 
widely distributed species is Thyreocoris ater (Fig. 457). Another 
species often found on berries is T. pulicarins; this species is some- 
times a serious celery pest. It is shiny black and has a white stripe 
on each side of the body; it measures 3 mm. in length. 



Family SCUTELLERID^ 
The Shield-hacked Bugs 
The members of this family are turtle-shaped bugs; that is, the 




HEMIPTERA 



393 



body is short, broad, and ver\^ convex. The scutellum is very 
covering nearly the whole of the abdomen. The 
lateral margins of the scutellum are not furnished 
with grooves for receiving the edges of the hemelytra 
as is the case in the two preceding families. The 
tibise are smooth or furnished with small spines. 
Figure 458 represents Eurygdster alterndtus somewhat 
enlarged, and serv^es to illustrate the typical form of 
members of this family. 

The family is represented in this country b}' 
fourteen genera including twenty-six species. I have 
met no account of any of our species occurring in 
sufficient numbers to be of economic importance. 



large, 




CHAPTER XXI 
ORDER HOMOPTERA* 

Cicadas, Leaf-Hoppers, Aphids, Scale-Bugs, and others 

The winged members of this order have four wings, except in the 
family Coccidce; the wings are of the same thickness throughout, and 
usually are held sloping at the sides of the body when at rest. The 
mouth-parts are formed for piercing and sucking; the beak arises from 
the hind part of the lower side of the head. The metamorphosis is gradual 
except in some highly specialized forms. 

Although the Homoptera is a well-defined order, the families of 
which it is composed differ greatly in the appearance of their members. 
For this reason there is no popular name that is applied to the order 
as a whole. 

The Homoptera was formerly regarded as a suborder of the Hemip- 
tera, that order being divided into two suborders, the Heteroptera 
and the Homoptera. But these two groups of insects differ so mark- 
edly in structure that it seems best to regard them as distinct orders. 
The Hemiptera is, therefore, restricted to what was formerly known 
as the suborder Heteroptera, and the suborder Homoptera is raised 
to the rank of a separate order. 

The wings of the Homoptera are usually membranous, but in 
some the front wings are subcoriaceous. In these cases, however, they 
are of quite uniform texture throughout, and not thickened at the 
base as in the Hemiptera. 

Many wingless forms exist in this order; in the family Coccidas 
the females are always wingless; and in the family Aphididas the 
males may be either winged or wingless, while the sexually perfect 
females and certain generations of the agamic fem^ales are wingless. 
In the Coccidas the males have only a single pair of wings, the hind 
wings being represented by a pair of club-like halteres. Each of 
these is furnished with a bristle, which is hooked and fits in a pocket 
on the hind margin of the fore wing of the same side. 

In several of the families of the Homoptera the wing-venation is 
greatly reduced; and even in the case of the more generalized forms, 
if only the wings of adults be studied the venation of these wings 
appears to depart widely from the hypothetical primitive type; 
but by examining the tracheae that precede the wing-veins in the 
wings of the nymphs, it is easy to determine the homologies of the 
wing-veins. This has now been done in the case of representatives of 
each of the families. The most generalized condition was found in 
the wings of a cicada, which will serve as the type of homopterous 
wing-venation. 

*Hom6ptera: homos (6/u6s), same, pteron (irTepdv), a wing. 

(394) 



HOMOPTERA 



395 



Figure 459 represents the tracheation of the fore wing of a 
young nymph of a cicada. The dotted Hne a-h indicates approximate- 
ly the line along which 
the hinge of the wing 
of the adult is formed. 
In this wing the only 
departures from the 
typical branching of 
the tracheee are the 
following: trachea Ri 
coalesces with the ra- 
dial sector to a point 
beyond the separation 
of trachea R 1+5 from 
the sector; the first 
anal trachea coalesces 
with trachea Cu for a 
short distance; and 
the second and third 
anal tracheae are unit- 
ed at the base. These 
differences are remark- 
ably slight compared with the great changes that have taken place 
in the specialization of the mouth -parts and other organs of the 
adult cicada. 

Figure 460 represents the fore wing of a mature nymph of a cicada. 
In this wing trachea Ri is completely aborted. In fact one of the 




Fig. 459. — Tracheation of a fore wing of a young 
nymph of a cicada. 




Fig. 460. — Tracheation of a fore wing of a mature nymph of a cicada. 



most characteristic features in the venation of the Homoptera, 
and of the Hemiptera also, is the absence or very great reduction 
of vein Ri in the adult wings of most members of these two orders. 
In the stage represented in this figure the developing cross-veins 
appear as pale bands. 



396 



AN INTRODUCTION TO ENTOMOLOGY 



Figure 461 represents the wings of an adult cicada. In this figure, 
where the veins are not numbered their homologies are indicated by 
the numbering of the cells behind them. In the adult wing there 
is a massing of several veins along the costal margin of the wing, 
and the cross-veins have the same appearance as the branches of 
the primary veins. 

Further details regarding the development of the wings of a cicada, 
and accounts of the development of the wings of representatives 
of other families of the Homoptera, are given in "The Wings of 
Insects" (Comstock '18). 

In the Homoptera the front part of the head is bent under and 
back so that the beak arises from the hind part of the lower side of 
the head. There is no distinct neck; and so closely is the head 
applied to the thorax that usually the front coxas are in contact 




The wings of a cicada. 



with the sides of the head, and in many forms the beak appears to 
arise from between the front legs. 

The mouth-parts are formed for piercing and sucking. The 
piercing organs consist of four long, bristle-like setae, the mandibular 
and maxillary setse; these are enclosed in a long, jointed sheath, 
which is the labium. The labium and the enclosed setee constitute 
what is commonly termed the beak. 

The beak, however, corresponds to only a portion of the mouth- 
parts of a chewing insect, each mandibular and maxillary seta being 
only a part of a mandible or maxilla; in each case another part of 
the organ enters into the composition of the head-capsule. 

As an example of the homopterous type of head and mouth-parts 
those of a cicada are probably the most available, on account of the 
large size of these insects and the comparative ease with which the 



HOMOPTERA 397 

parts of the head can be distinguished. Figure 462 represents a lateral 





Fig. 462. — Head and prothorax of a Fig. 463. — Head of a cicada, front view: 

cicada, lateral aspect: a, antenna; md, mandibular seta; mx, maxillary 

c, clypeus; e, compound eye; ep, seta; other letters as in Fig. 462. 

epipharynx; /, labrum; o, ocelli; 2, (After Marlatt, with changes in the 

3, second and third segments of the lettering.) 
labium. (After Marlatt, with changes 
in the lettering.) 

view of the head and prothorax of a cicada, and Figure 463 a front view. 
The corresponding parts are 
lettered the same in the two 
figures. 

The compound eyes 
(Figs . 46 2 and 463 , ^) , the an - 
tennse (Figs. 462 and 463 , a) , 
and the three ocelli (Figs. 
466 and 467, o),can be easily 
recognized and need not be 
described in detail. 

The front is a small scle- 
rite near the stunmit of the 
head. It can be most easily 
recognized by the fact that 
it bears the median ocellus. 
In the adult insect the su- 
ture between it and the ver- 
tex is indistinct; but in the exuviae of a nymph, where the epicranial 
suture has been opened by the emergence of the adult, the outline 
of this sclerite is evident (Fig. 464). In many homopterous insects 
the front is vestigial or wanting. 

The vertex (Figs. 462 and 463, v) bears the paired ocelli. 

The clypeus (Figs. 462 and 463, c) is very large, occupying the 
greater part of the anterior surface of the head. In several of the 




Fig. 464. — Part of the exuviae of the head of 
a nymph of a cicada: a, antennas; as, 
antennal sclerite; c, clypeus; e, e, com- 
pound eyes; /, front; v, v, vertex. (After 
Berlese.) 



398 



AN INTRODUCTION TO ENTOMOLOGY 



CO - 



published accounts of the head of homopterous insects the clypeuS 
has been incorrectly identified as the front. 

The lahnmi (Figs. 462 and 463, /) is joined to the lower end of the 
clypeus; at its distal end it forms a sheath covering the base of the 
labium and the enclosed setae. This part is described as the clypeus 
by those who have incorrectly identified the clypeus as the front. 
The epipharynx (Figs. 462 and 463, ^) arises at its normal position 
on the ental surface of the labrum; but it is greatly developed and 
projects beyond the end of the labrum. The projecting part has been 

mistaken for the labrum by 
some writers, those who 
have failed to recognize the 
front and have termed the 
clypeus the front and the 
labrum the clypeus. 

The mandibular sclerites 
are easily recognized in the 
cicada. On each lateral as- 
pect of the head there are 
two quite distinct sclerites; 
the one that is next to the 
clypeus and the base of the 
labium is the mandibular 
sclerite(Figs.462and463,:i;), 
This sclerite is termed the 
lora by some writers on the 
Homoptera. 

The mandibular sclerites 
are believed to be in each 
case the basal part of a man- 
dible. They were first rec- 
ognized as such by Profes- 
sor J. B. Smith ('92); and 
this conclusion has been 
adopted by Marlatt ('95), 
Heymons ('99), Meek ('03), 
Berlese ('09), and Bugnion 
and Popoff ('11). On the 
other hand, Muir and Ker- 
shaw ('12) regard the lors as "lateral developments of the clypeal 
region" and not parts of mandibles. 

The structure of the mandible as a whole has been worked out by 
Meek ('03) and is shown in the left half of Figure 465. Within the 
cavity of the head the maxillary seta is enlarged, and to it are attached 
a retractor muscle {mdr) and a protractor muscle (mdp) . The seta is 
attached to the dorsal end of the mandibular sclerite (Fig. 465, mds) 
by a quadrangular sclerite (Fig. 465, co). 

The maxillary sclerites (Figs. 462 and 463, y) are closely parallel 
with the mandibular sclerites, but extend farther down, joining the 




Fig. 465. — Caudal view of the head of a cicada, 
with part of the head-capsule and muscles re- 
moved so as to show the left mandible and 
the right maxilla. (Prom Meek.) 



HO MOP T ERA 



399 



terminal part of the labrum. Each maxillan- sclerite is a part of a 
maxilla. This is clearly shown by the fact that in the embryo each 
maxilla is at first a bilobed appendage; from one of these lobes the 
maxillary sclerite is developed, and from the other the maxillary seta 
(see Heymons '99). In the adult insect the maxillary sclerites are 
not separated from the epicranium by sutures as are the mandibular 
sclerites (Figs. 462 and 463). 

The form and relations of the different parts of a maxilla, as 
worked out by Meek ('03), are shown in the right half of Figure 465. 
From the enlarged base of the maxillary seta a crescent -shaped 
sclerite (Fig. 465, ca) extends to the maxillar\^ sclerite (Fig. 465, mxs). 
In this figure the maxillary retractor muscles {mxr), the maxillary 
protractor muscles (mxp), and a tendon (mc) connecting the crescent- 
shaped sclerite with the tentoriim:i, are also represented. 

It is interesting to note the similarity in the structure of the 
mandibles and the maxillae. Each consists of a basal part which forms 
a portion of the wall of the head; a terminal piercing organ, the 
seta; and a sclerite connecting these two parts. 

The labium forms the outer wall of the beak; it consists of three 
segments; the second and third are lettered in Figures 462 
and 463. The proximal segment is probably homologous with the 
submentum of the chewing insect mouth; the second segment, with 
the menttmi; and the third segment, with the ligula (see footnote, 
page 354). The dorsal surface of the labium, which is the lower 
surface, isdeeply 

grooved, forming a 

channel which enclos- 
es the mandibular and 
maxillary setae. 

The labium, which 
is all that is commonly 
seen of the beak in 
either hemipterous or 
homopterous insects, 
is not a piercing or- 
gan; it is not pushed 
into the food sub- 
stance of the insect, 
but serves merely as a 
sheath for the mandib- 
ular and maxillary 
setse, which are the 
piercing organs and which are worked by the protractor and retractor 
muscles within the head (Fig. 465). 

Figure 466 represents a cross-section of the third segment of the 
beak of a cicada as figured by Meek ('03), and shows the relation of 
the labitmi to the mandibular and maxillar}^ setae. Each seta is 
crescent-shaped in cross-section; the mandibular setae lie outside of 
the maxillary setae; the maxillary setae, which extend side by side at 




Fig. 466. — Cross-section of the third segment of the 
beak of a cicada: lah, labium; md, mandibular 
seta; mx, maxillary seta; /, /, lumina in the seta. 
(From Aleek.) 



400 AN INTRODUCTION TO ENTOMOLOGY 

the base of the beak, are twisted so that at this point one lies above 
the other. The two are fastened together by interlocking grooves 
and ridges ; and between them is a channel for the passage of the food. 
Within each of the four setae, there is a lumen (Fig. 466, /, /). 

The hypopharynx is a funnel-shaped, chitinized organ found near 
the base of the ental surface of the labitmi, at the end of the phar\'nx. 

The nature of the metamorphosis differs to a considerable degree 
in the different families; in most cases it is gradual, but marked 
modifications of this type have been developed in the Aleyrodidee 
and in the Coccidae. 

The members of this order feed on vegetation and to it belong 
some of our more important insect pests. 

This order includes ten families, which are designated as follows : 

The Cicadas, Family Cicadid^, p. 401. 

The Spittle-insects, Family Cercopid^, p. 402. 

The Tree-hoppers, Family Membracid^, p. 404. 

The Leaf-hoppers, Family Cicadellid^, p. 406. 

The Lantern-fly Family, Family Fulgorid^, p. 408. 

The Jumping Plant-hce, Family Chermid^, p. 410. 

The Typical Aphids, Family Aphidid^, p. 415. 

The Adelgids andthePhylloxerids, Family Phylloxerid^, p. 428. 

The Aleyrodids, Family Aleyrodid^, p. 437. 

The Scale-bugs, Family Coccid^, p. 440. 

TABLE FOR DETERMINING THE FAMILIES OF THE HOMOPTERA 

A. Beak evidently arising from the head; tarsi three- jointed; antennas minute, 
bristle-Hke. 

B. With three ocelH, and the males with musical organs. Usually large 
insects, with all the wings entirely membranous, p. 401 Cicadid^ 

BB. Ocelli only two in number or wanting; males without musical organs. 
C. Antenn-^ inserted on the sides of the cheeks beneath the eyes. p. 408 

FULGORID^ 

CC. Antennae inserted in front of and between the eyes. 
D. Prothorax not prolonged above the abdomen. 

E. Hind tibiae armed with one or two stout teeth, and the tip crowned 

with short, stout spines, p. 402 Cercopid^ 

EE. Hind tibiae having a row of spines below, p. 4o6.Cicadellid^ 
DD. Prothorax prolonged into a horn or point above the abdomen, p. 404 

Membracid^ 

AA. Beak apparently arising from between the front legs, or absent ; tarsi one- or 
two- jointed; antennae usually prominent and threadlike, sometimes 
wanting. 
B. Tarsi usually two- jointed; wings when present four in number. 
C. Wings transparent. 

D. Hind legs fitted for leaping; antennas nine- or ten-jointed, p. 410.. 

Chermid^ 

DD. Legs long an slender, not fitted for leaping; antennas three- to 

seven-jointed. 412 Superfamily Aphidoidea 

CC. Wings opaque, whitish; wings and body covered with a whitish 
powder, p. 437 Aleyrodids 



HOMOPTERA 401 



BB. Tarsi usually one-jointed; adult male without any beak, and with only 
two wings; female wingless, with the body either scale-like or gall-Hke in 
form, or grub-like and clothed with wax. The waxy covering may be in the 
form of powder, of large tufts or plates, of a continuous layer, or of a . „ 
thin scale beneath which the insect lives, p. 440 CocciDiE ^iC^/fl/ "\ 



F MiLY CICADID^ \»i\ 

The Cicadas \j^ 

The large size and well-known songs of the more common species 
of this family render them familiar objects. It is only necessary to 
refer to the periodical cicada and to the harvest- 
flies, one of which is represented by Figure 467, 
to give an idea of the more striking character- 
istics of this family. We have species of cicadas 
much smaller than either of these; but their 
characteristic form is sufficient to distinguish 
them from members of the other families of 
this order. 

The species are generally of large size, with 
a subconical body. The head is wide and blunt, 
with prominent eyes on the outer angles, and 
three bead-like ocelli arranged in a triangle be- 
tween the eyes. The stntcture of the mouth- 
parts is described on an earlier page and illus- 
trated by several figures; and the form and 
venation of the wings are shown by Figure 461. 
But the most distinctive peculiarity is the form „. „ ., . , . 

of the musical organs of the males ; an example of ^ '^„et ~ "" 
these is described and figured on pages 89 to 9 1 . 

The family Cicadid^ is well represented in this country ; seventy- 
four species, representing sixteen genera, are now listed from our 
fauna. The two following species will serve as illustrations. 

There are several species of cicadas that are commonly known as 
dog-day cicadas or harvest -flies ; the most abundant of these is the 
species that has received the popular name of the lyreman; this is 
Tih'icen linnet (Fig. 467). The shrill cry of this species, which is the 
most prominent of the various insect sounds heard during the latter 
part of the summer, has brought its author into prominent notice. 
This insect varies both in size and colors. It commonly measures 50 
mm. to the tip of the closed wings; it is black and green, and more or 
less powdered with white beneath. The transformations of this 
insect are similar to those of the following species, except that it 
probably completes its development in a much shorter period. It 




402 AN INTRODUCTION TO ENTOMOLOGY 

differs also in seldom, if ever, occurring in sufficient numbers to be 
of economic importance ; but a brood of it appears each year. 

The member of this family that has attracted most attention is 
the periodical cicada, Tihicina septcndecim. This species is commonly 
known as the seventeen-year locust; but the term locust when applied 
to this insect is a misnomer, the true locusts being members of the 
order Orthoptera. The improper application of the term locust to 
this species was doubtless due to the fact that it appears in great 
swarms, which reminded the early observers in this country of the 
hordes of migratory locusts or grasshoppers of the Old World. This 
species is remarkable for the long time required for it to attain its 
maturity. The eggs are laid in the twigs of various trees ; the female 
makes a series of slits in the twig, into which the eggs are placed. 
vSometimes this cicada occurs in such great mmibers that they seriously 
injure small fruit trees, by ovipositing in the twigs and smaller 
branches. The n^-mphs hatch in about six weeks. They soon volun- 
tarily drop to the ground, where they bury themselves. Here they 
obtain nourishment by sucking the juices from the roots of forest and 
fruit trees. And here they remain till the seventeenth year following. 
They emerge from the ground during the last half of Alay, at which 
time the empty pupa-skins may be found in great numbers, clinging 
to the bark of trees and other objects. It is at this period that the 
cicadas attract attention by the shrill cries of the m.ales. The insects 
soon pair, the females oviposit, and all disappear in a few weeks. 

More than twenty distinct broods of this species have been traced 
out; so that one or more broods appear somewhere in the United 
States nearly every year. In many localities, several broods co-exist; 
in some cases there are as many as seven distinct broods in the same 
place, each brood appearing in distinct years. There is a variety of 
the species in which the period of development is only thirteen years. 
This variety is chiefly a southern form, while the seventeen-year 
broods occur in the North. 



Family CERCOPID^ 
The Spittle-Insects cr Frog-Hoppers 

During the summer months one often finds upon various shrubs, 
grass, and other herbs, masses of white froth. In the midst of each of 
these masses there lives a young insect, a member of this family. 
In some cases as many as four or five insects inhabit the same mass 
of froth. It is asserted that these insects undergo all their trans- 
formations within this mass; that when one is about to molt for the 
last time, a clear space is formed about its body and the superficial 
part of the froth dries, so as to form a vaulted roof to a closed chamber 
within which the last molt is made. 

The adult insects wander about on herbage, shrubs, and trees. 
They have the power of leaping well. The name frog-hoppers has 



IIOMOPTERA 403 

doubtless grown out of the fact that formerly the froth was called 
"frog-spittle" and was supposed to have been voided by tree-frogs 
from their mouths. The name is not, however, inappropriate, for 
the broad and depressed form of our more common species is somewhat 
like that of a frog. 

The origin and formation of the froth of spittle-insects has been 
discussed by many writers. Guilbeau ('08) found by many experi- 
ments that the froth is derived from two sources. The greater part 
of the fluid is voided from the anus; to this fluid is added a mucilagi- 
nous substance which renders it viscous and causes the retention of 
air bubbles, which are introduced into it by the insect by means of its 
caudal appendages. The mucilaginous substance is the excretion of 
large hypodermal glands, which are in the pleural region of the 
seventh and eighth abdominal segments. These are known as the 
glands of Batelli; they open through numerous minute pores in the 
cuticula. 

It is evident that the covering of froth protects the spittle-insects 
from parasites and other enemies. 

In this family the antennas are inserted in front of and between 
the eyes; the prothorax is not prolonged back of the abdomen, as in 
the Membracidas ; the tibise are armed with one or two 
stout teeth, and the tip is crowned with short, stout 
spines, as shown in Figure 468. 

The Cercopidas is represented in our fauna by six 
genera, which include twenty-five species. The follow- Fig. 468.-1,5- 
ing species will serve as examples. p y r m a 

One of the more common and very widely distribut- ^^^^ ''^nlin- 
ed species is Lepyronia quadranguldris (Fig. 468). The ral size, and 
adult of this species is a brownish insect, densely one tibia en- 
covered with microscopic hairs, and black beneath; larged. 
the hemelytra are marked with two oblique brown bands, which 
are confluent near the middle of the costal margin; the humeral 
region is dusky; and the tip of each hemelytron is marked with a 
small blackish curve; the ocelli are black, but indistinct. This 
species measures from 6 mm. to 8 mm. in length. 

Somewhat resembling the preceding species, and also common 
and widely distributed, is Aphrophora quadranotdta. In this species 
the body is pale; the hemelytra are dusky, each with two large hya- 
line costal spots, margined with dark brown ; the ocelli are blood-red ; 
and the head and pronotimi are furnished with a slightly elevated, 
median, longitudinal line. 

To the genus Clastopiera belong certain other common members 
of this family. In this genus the body is short and plump, some- 
times nearly hemispherical; the species are small, our common forms 
ranging from 3 mm. to 6 mm. in length. Clastopiera proteus is a 
conspicuous species on account of its bright yellow markings. It 
varies greatly in color and markings; but the most striking forms 
are black, with three transverse yellow bands, two on the head and 
one on the thorax, and with the scutellum and a large oblique band 



404 



AN INTRODUCTION TO ENTOMOLOGY 



on each hemelytron yellow. Another common species is Clasloptera 
ohtusa. This occurs on black alder in summer and autumn. It is of a 
claret-brown color above, marked with two pale bands on the vertex, 
two on the prothorax, and a wavy, broader band on the hemelytra. 
The membrane is often whitish, the waved band is extended exteriorly, 
and there is a pale V-shaped figure on the end of the scutellum. 

Family MEMBRACID.^ 

The Tree-Hoppers 





Spongophorus hallista; B, Spongophorns 



The most useful character for distinguishing members of this 
family is the prolongation of the prothorax backward above the 

abdomen; some- 
times it extends 
back to the tip of 
the abdomen and 
completely cov- 
ers the wings. 
This develop- 
ment of the 
prothorax re- 
sembles that 
which occurs in 
the pigmy lo- 
custs, the sub- 
familyAcrydiinag 
of the order Or- 

thoptera. In many of the Membracidae, however, the prothorax is 
not only prolonged backward but is extended sidewise or upwards, 
with the result that in some cases the insect presents a most bizarre 
appearance ; this is especially true of certain tropical forms ; Figure 469 
represents two species found in Central America. 

Many species of the Membracidae live upon bushes or small 
trees; others inhabit grass and other herbaceous plants. Although 
these insects subsist upon the juices of plants, they rare- 
ly occur in sufficient numbers to be of economic impor- 
tance. Sometimes the females injure young trees by lay- 
ing their eggs in the bark of the smaller branches and in 
buds and stems. Many members of this family excrete 
honey -dew and are attended by ants, especially in the 
nymphal stages, as are the aphids. The adults are good 
leapers ; hence the common name tree-hoppers. 

This family is well represented in this countr\' ; 
one hundred eighty-five species, representing forty-three genera, are 
now listed. Among our more common species are the following. 

The Buffalo tree-hopper, Ceresa hubalus. — The popular name of 
this species refers to the lateral prolongations of the prothorax, 
which suggest the horns of a buffalo (Fig. 470). The life-history of 



f 



Fig. 470.— Cer- 
esa hubalus. 



HOMOPTERA 



405 



this insect has been worked out by Funkhouser ('17). The n}TTiphs 
feed on succulent herbs, particularly sweet clover; the eggs are laid 
on young trees, particularly elm and apple, the stems of which are 
injured by the egg-punctures. Oviposition occurs most commonly 
in early September, at Ithaca, N. Y. The eggs hatch early in the 
following May. The young nymphs leave the trees on which the 
eggs were deposited and migrate to succulent weeds. The early life 
of the adult is spent on the weeds ; but later the females migrate to 
trees for egg-laying. 

The two-homed tree-hopper, Ceresa dicer os.- — This species re- 
sembles the buffalo tree-hopper in size and form. It is a pale dirty 
yellow, spotted with brown; the lateral and caudal aspect of each 
horn is brown; the caudal tip of the prothorax, and a large spot 
midway between the tip and the horns, are also brown. The insect is 
densely clothed with hairs. It is common on black elder, Sambucus 
canadensis. Funkhouser followed the life-history from the egg to the 
adult on this plant. The eggs are laid about the middle of August 
in the second-year stems, and hatch about the middle of May. 

The two-marked tree-hopper, Enchendpa binotdta.- — In this spe- 
cies the pronotum is prolonged in an upward- and forward- projecting 
horn (Fig. 471). This insect is very abundant on trees, 
shrubs, and vines. It is gregarious, and both adult and 
immature forms are found clustered together. The 
eggs are usually laid in frothy masses, which are very 
white and appear like wax. Funkhouser states that 
a variety of this species found on butternut lays its eggs 
in the buds and does not cover them with the heavy 
froth. The specific name of this species refers to the 
fact there are two yellow spots on the dorsal line of the pronotum. 
Another very common species, and one that is closely allied to the 
preceding, is Campylenchia Idtipes. This is brownish, 
unspotted, and has a rather longer horn than that 
of the two-marked tree-hopper; but it varies much 
in color and in the length of the pronotal horn. This 
is a grass-inhabiting species and is common in pastures 
and especially on alfalfa. It is often taken by sweeping. 
Telamona. — To this genus belong our humpback 



Fig. 471.— £w- 
chenopa bi- 
notata. 




Fig. 472. — Tel- 
amona. 




406 AN INTRODUCTION TO ENTOMOLOGY 

forms (Fig. 472), of which about thirty species have been found 
in our fauna. They Hve chiefly on oaks, hickories, basswood, and 
other forest trees. The adults generally rest singly on the limbs 
and branches of the trees; they are strong flyers and are difficult to 
capture. The immature forms keep together in small groups. 

Figure 473 represents a front viev/ of several membracids in our 
collection. 

Family CICADELLID^* 

J he Leaf -Hoppers 

This family is a very large one, and it is also of considerable 
economic importance; for it includes a ntimber of species that are 
very injurious to cultivated plants. The members of it are of small 
or moderate size. The antennae are inserted in front of 
and between the eyes; the pronotum is not prolonged 
above the abdomen; and the hind tibiae are nearly 
or quite as long as the abdomen, curv^ed, and 
armed with a row of spines on each margin. The form 
and armature of the hind tibiae are the most salient 
characters of this family. The form of the body is 
commonly long and slender, often spindle-shaped; but 

"_ some are plump. 

^fcc/J/ exitt- These insects are able to leap powerfully; and, as 
osus. they are more often found on the leaves of herbage 

and on grass than elsewhere, they have been named leaf-hoppers. 
They infest a great variety of plants; some of them are important 
pests in gardens, orchards, and vineyards; but they are most destruc- 
tive as pests of grains and grasses. Although this is true, much 
less attention has been paid to injuries caused by them to grains 
and grasses than to those inflicted upon vineyards and rose bushes. 
More than seven hundred species, representing about seventy 
genera, have been found in the United vSiates and Canada. Among the 
more important members of the family from an economic standpoint 
are the following. 

The destructive leaf-hopper, Eiiscelis exitiosus, which is repre- 
sented, greatly enlarged, in Figure 474, sometimes infests winter 
wheat to a serious extent. It is a widely distributed species, its 
range including nearly the whole of the United States. It is a 
small, active, brownish insect, which measures with its wings folded 
about 5 mm. in length. It injures grass or grain b}^ piercing the 
midrib of the leaf and sucking the juices from it. 

The grape-vine leaf -hopper, Erythroneura comes, is a well-known 
pest which infests the leaves of grape, in all parts of this country 
where this vine is grown. It is a little more than 3 mm. in length, 
and has the back and wings marked in a peculiar manner with yellow 
and red. In the winter the darker markings are a dark orange-red, 
but after feeding has been resumed for a short time in the spring 
they change to a light lemon-yellow. The darker markings on the 

*This family has been commonly known as the Jassidae, but Cicadellidae is the 
older name. 



HO MO PT ERA 



407 




adults var>^ so much that eleven distinct varieties are now recognized ; 
two of these are represented at b and c in Figure 475. 

The rose leaf-hopper, Empoa toscb, is a well-known pest of the 
rose. Swarms of these insects may be found, in various stages of 
growth, on the leaves of 
the rose-bush through 
the greater part of the 
summer, and their nu- 
merous cast skins ma}^ be 
seen adhering to the low- 
er sides of the leaves; in 
fact attention is most fre- 
quently called to this 
pest by these white ex- 
uviae. The adult meas- 
ures less than 3 rrsn. in 
length. Its body is yel- 
lowish white, its wings 
are white and transpar- 
ent, and its eyes, claws, 
and ovipositor are brown. 

The apple leaf-hop- 
per, Enipodsca JahcB. — Al- 
though this species is 
named the apple leaf- 
hopper, it infests to an in- 
jurious extent man}^ dif- 
ferent plants, both cultivated and wild. Slingerland and Crosby ('14) 
state that it infests apple, currant, gooseberry, raspberry, potato, 
sugar-beets, beans, celery, grains, grasses, shade trees, and weeds. 
The adult insect measures about 3 mm. in length, and is of a pale 
yellowish green color with six or eight distinguishing white spots on 
the front margin of the pronotirm. 

The genus Drccailaccphala includes grass-green or pale green, 
spindle-shaped species, in which the head ai seen from above is long 
and triangular. One of the species, D. reticulata, sometimes greatly 
injures fields of grain in the South. 

The genus Oncometopia includes species in which the head is 

more blunt than in the preceding genus and is wider across the eyes 

than the thorax. O. tmddta (Fig. 476) is a common 

/^^ species. Its body, head, fore part of the thorax, scutel- 
^./^^^ lum, and legs are bright yellow, with circular lines of 
yWl black on the head, thorax, and scutellimi. The fore 
^ wings are bluish purple, when fresh, coated with 
whitish powder. It measures 12 mm. in length. It is 
said to lay its eggs in grape canes, and to puncture 
with its beak the stems of the bunches of grapes, 
causing the stems to wither and the bunches to drop off. 
One division of this family, the subfamily Gyponinge, includes forms 
which resemble certain genera belonging to the Cercopidsby their 



Fig. 475. — Ery'.hroiieiira cor.zes: a and h, female 
and male of the typical corr.es variety; c, the 
vi'As variety. (From Slingerland.) 



Fig. 476. — On ■ 
come t o pia 
undata. 



408 AN INTRODCUTION TO ENTOMOLOGY 

plump proportions. Among these are Penthima americdna, which is 
a plump, short-bodied insect, resembling a Clastoptera; and the genus 
Gypona includes a large niimber of species, some of which resemble 
very closely certain species of Aphrophora. A glance at the posterior 
tibiae of these leaf-hoppers will enable one to distinguish them from 
the cercopids, which they so closely resemble. 

Methods of combating leaf-hoppers. — Leaf-hoppers, being sucking 
insects, are fought with contact insecticides. But it is difficult to 
destroy the adults, for they are so well-protected by their wings that 
applications strong enough to kill them are liable to injure the foliage 
of the host-plant; and, too, they are very active and fly away when 
approached. The most effective remedial measures are those directed 
against the nymphs. These consist of the use of some spray, as a ten- 
per-cent. kerosene emulsion or a soap solution made by dissolving one 
pound of soap in six or eight gallons of water, or a solution made of 
one ounce of "black leaf 40" tobacco extract and six gallons of water 
in which has been dissolved a piece of soap the size of a hen's egg. 
The application should be so applied as to wet the lower surface of 
every leaf. 

Family FULGORID^ 
The Lantern-Fly Family 

This family is remarkable for certain exotic forms which it includes. 
Chief among these is the great lantem-fiy of Brazil, Laterndria phos- 
phorea. This is the largest species of the family and is one of the 
most striking in appearance of all insects (Fig. 477). It has immense 
wings, which expand nearly six inches; upon each hind wing there is 




Fig. 477. — The lantern-fly, Lalernaria phosphorea. 

a large eye-like spot. But the character that makes this insect es- 
pecially prominent is the form of the head. This has a great bladder- 
like prolongation extending forward, which has been aptly compared 
to the pod of a peanut. Maria Sibylla Merian, a careful observer, 
who wrote more than two hundred years ago (1705), stated that this 
prolongation of the head is limiinescent. This statement was ac- 
cepted by Linnseus without question ; and he made use of names for 
this and some allied species, such as laternaria, phosphorea, candelar- 
ia, etc., to illustrate the supposed light-producing powers of these 
insects. The common name lantern-fly is based on the same belief. 



HOMOPTERA 



409 




(Aftei 




Fig 

Scolops 



479-- 



The Brazilian lantern-fly has been studied by many more recent 
observers, and all have failed to find that it is luminescent. It may 
be that the individuals observed by Madame Merianwere infested 
by luminescent bacteria, 
as has been observed to 
be the case occasionally 
in certain other insects. 
No member of this fam- 
ily is known to be kmii- 
nescent. 

The Chinese candle- Fig. 478. — Antenna of Megamelus nottila 
fly, Fulgoria candeldria, Hansen.) 
is another very promi- 
nent member of this family, which is commonly represented in col- 
lections of exotic insects and is often figured by the Chinese. This 
too has been reputed to give light. 

Certain fulgorids found in China excrete large 
quantities of a white, flocculent wax, which is used by 
the Chinese for candles and other purposes. 

There does not seem to be any typical form of the 
body characteristic of this family. The different genera 
differ so greatly that on superficial examination they 
appear to have very little in common. The most 
useful character for recognizing, these insects is the 
form and position of the antennae. These are situated 
on the side of the cheeks beneath the eyes; the two 
proximal segments, the scape and pedicel, are stout (Fig. 478); the 
clavola consists of a small, nearly pear-shaped basal segment and a 
slender, segmented or un- 
segmented, bristle-like ter- 
minal part. The pedicel is 
provided with numerous 
sense-organs. 

So far as numbers are 
concerned this family is 
well represented in our 
fauna, three hundred fifty- 
seven species and seventy- 
seven genera having been 
listed; but our species are 
all small compared with the 
exotics mentioned above. The following of our native genera will 
serve to illustrate some of the variations in form represented in this 
country. The species all feed on the juices of plants. 

Scolops.- — In this genus the head is greatly prolonged (Fig. 479), as 
with the Chinese candle-fly. Our more common species, however, 
measure only about 8 mm. in length. 

Otiocerus. — In this genus the body is oblong; the head is com- 
pressed, with a double edge both above and below. Otiocerus coque- 
bertii (Fig. 480) is a gay lemon-yellow or cream-colored species, with 




Fig. 480.- 
ler.) 



-Otiocerus coquehertii. (From Uh- 



410 



AN INTRODUCTION TO ENTOMOLOGY 



wavy red lines on the fore wings. It measures about 8 mm. to the 
tips of the wings, and Hves upon the leaves of grape-vines, oaks, and 
hickory. 

Ormenis. — In our common representatives 
of this genus the wing -covers are broad, and 
closely applied to each other in a vertical 
position ; they are more or less truncate, and 
give the insects a wedge-shaped outline. 0. 
septentriondlis (Fig. 481) is a beautiful, pale 
green species powdered with white, which 
feeds on wild grape-vines, drawing nourish- 
ment from the tender shoots and midribs of the 
leaves, during its young stages. 




Fig. 481. — Ormems sep- 
tentrionalis. 



Family CHERMID.E* 
The Jumping Plant-Lice 

The jumping plant-lice are small insects ; many of them measure 
less than 2 mm. in length ; and the larger of our species, less than 5 mm. 
They resemble somewhat the winged aphids; but they 
look more like miniature cicadas (Fig. 482). They 
differ from aphids in the firmer texture of the body, 
in the stouter legs, in having the hind legs fitted for 
jumping, and in the antennge being ten-jointed or 
rarely nine- or eleven-jointed. The terminal segment 
of the antenucC bears two thick setae of unequal length. 
Both sexes are winged in the adult. The front 
wings are ample, and, while often transparent, are inuch 
thicker than the hind wings. The homologies of the 
wing-veins of the fore wings of Psyllia floccosa are indi- 
cated in Figure 4S3. 




Fig. 482.-P5W- 
lia. 




itf,+2 



Fig. 483. — The venation of a fore wing of Psy'dia floccosa. (x^fter Patch.) 
The beak is short and three-jointed. The basal segment of the 
beak is held rigidlv between the fore coxae. 



*This family has been quite commonly known as the PsyUidae, a result of an 
incorrect application of the name Chermes to a genus of the Phylloxeridse. 



HOMOPTERA 



411 



The jumping plant-lice are very active little creatures, jumping 
and taking flight when 
disturbed; but their 
flight is not a prolonged 
one. They subsist en- 
tirely upon the juices of 
plants; some species 
form galls ; but it is rare 
that any of the species 
appear on cultivated 
plants in sufficient num- 
bers to attract attention, 
except in case of the pear- 
tree Psylla. 

The family Chermi- 
das is of moderate size; 
in our latest list onc- 
hundrcd thirty-seven 
species representing 
twenty-four genera, are 
enumerated from our 
fauna. The two fol- 
lowing species will ser^^e 
to illustrate variations in 
habits of these insects. 

Pachypsylla celtidis- 
mdmma. — This is a gall- 
making species which in- 
fests the leaves of hack- 
berry (Ccltis occidentalis). Figure 4S4 represents an infested leaf 
with galls, and a single gall and a nymph enlarged. The adult insect 
(Fig. 485) has a wing expanse of about 6 mm. 

The pear-tree psyllia, Psyllia pyricola. — This is our most impor- 




Fig. 484. — Gall of Pachypsylla celtidis-niamma: 
a,leaf with galls, from under-side; ^, section of 
gall enlarged and insect in cavity; c, nymph, 
enlarged . (From Riley . ) 




Fig. 485. — Pachypsylla celtidis-mamma. (From 
Packard.) 

Fig. 486. — Psyllia 
pyricola. 

tant species from an economic standpoint, being a serious enemy of 
the pear. It is a small species (Fig. 486) ; the summer generations 



412 AN INTRODUCTION TO ENTOMOLOGY 

measure to the tips of the folded wings from 2.1 mm. to 2.8mm., the 
hibernating form 3.3 mm. to 4 mm. The general color is light 
orange to reddish brown, with darker markings. The eggs are laid 
early in the spring in the creases of the bark, in old leaf-scars, and 
about the base of the terminal buds. The young n^Tnphs migrate 
to the axils of the leaf petioles and the stems of the forming fruit; 
later they spread to the under side of the leaves. They secrete large 
quantities of honey -dew, upon which a blackish fungus grows; this 
is often the first indication of the presence of the pest. There are at 
least four generations each year. Badly infested trees shed their 
leaves and yoimg fruit in midsummer. In some cases orchards have 
been so badly injured by this pest that they have been cut down by 
their owners. 

The methods of control that are recommended are the following : 
the scraping off of the rough bark from the trunks and larger branches 
of the trees and burning it, in order to destroy the hibernating adults ; 
and thorough spraying of the trees with kerosene emulsion or "black 
leaf 40" tobacco extract when the petals have fallen from the 
blossoms, in order to destroy the newly hatched nymphs; this spray- 
ing should be repeated in three or four days; later sprayings are 
not so effective on account of the protection afforded the insects by 
the expanded leaves and by their covering of honey-dew. 

A monograph of the North American species of this family has 
been pubHshed by Crawford ('14). 

SUPERFAMILY APHIDOIDEA 

The Plant-Lice cr Aphids and their Allies 

The plant-lice or aphids are well-known insects; they infest 

nearly all kinds of vegetation in all parts of the countr}'. Our most 

common examples are minute, soft -bodied, 

green insects, with long legs and antenna, 

which appear on various plants in the house 

and in the field. Usually, at least, in each 

species there are both winged and wingless 

forms (Fig. 487). There are many species 

of aphids, nearly all of which are of small 

Fig. 487.— A group of size; some measure less than i mm. in 

aphids. length; and our largest species, only 5 or 

6 mm. 

The body in most species is more or less pear-shaped. The 

winged forms have two pairs of delicate, transparent wrings. These 

are furnished with a few simple or branched veins; but the venation 

is more extended than in either of the two following families. The 

fore wings are larger than the hind wings; and the two wings of 

each side are connected by a small group of hamuli. The wings are 

usually held roof -like when at rest (Fig. 488, ab\ but are laid flat on the 

abdomen in some genera. The beak is four-jointed and varies greatl}- 




HOMOPTERA 



413 



in length ; in some species it is longer than the body. The antennae 
consist of from three to six segments; the last segment is usually 
provided with a narrowed prolongation (Fig. 488, aa). The first two 
segments of the antennas are always short, but the other segments 
show a great specific variation in length and are therefore very 
useful as systematic characters. Excepting the first two, the seg- 
ments of the antennas are usually provided with sense-organs, the 
sensoria, which vary in nimiber and shape in different species and are 




Fig. 488. — The melon aphis, Aphis gossypi: a, winged agamic female; aa, en- 
larged antenna of same; ab, winged agamic female, with wings closed, sucking 
juice from leaf; b, young nymph; c, last nymphal instar of winged form; d, 
wingless agamic female. (From Chittenden.) 



much used in the classification of these insects. On the back of the 
sixth abdominal segment there is, in many species, a pair of tubes, 
the cornicles, through which a wax-like material is excreted. In some 
genera these organs are merely perforated tubercles, while in still 
other genera they are wanting. It was formerly believed that the 
honey-dew excreted by aphids came from the cornicles ; for this 
reason they are termed the honey-tubes in many of the older books. 
The honey-dew of aphids is excreted from the posterior end of the 
alimentary canal. It is sometimes produced in such quantities that 
it forms a glistening coating on the leaves of the branches below the 
aphids, and stone walks beneath shade-trees are often densely spotted 



414 



AN INTRODUCTION TO ENTOMOLOGY 



with it. This honey-dew is fed upon by bees, wasps, and ants. The 
bees and wasps take the food where they find it, paying Uttle if any 
attention to its source ; but the ants recognize in the plant-Hce useful 
auxiharies, and often care for them as men care for their herds. 
This curious relationship is discussed later, under the head of Ants. 
In addition to honeydew, many aphids excrete a white waxy sub- 
stance. This may be in the form of powder, scattered over the 



Sc^R^M+Cu,^lstA 




Fig. 489. — The wings of Eriosoma americana. (From Patch.) 

surface of the body, or it may be in large flocculent or downy masses; 

ever}^ gradation between these forms exists. 

The superfamily Aphidoidea includes two families, the Aphididas 

and the Phylloxeridas. These two families differ in the life-histories 

of their species and in the venation of the wings of the winged forms, 

as follows : 

A. Only the sexually perfect females lay eggs; the parthenogenetic forms give 
birth to developed young, which, however, in some cases, are each enclosed in a 
pellicle. The radius of the fore wings is branched; and the outer part of the 
stigma is bounded behind by vein Ri (Fig. 489) Aphidid^ 

AA. Both the sexually perfect females and the parthenogenetic forms lay eggs. 
Vein Ri of the fore wings is wanting; and the outer part of the stigma is 
bounded behind by the radial sector (Fig. 490) Phylloxerid.,e 



Sc^R^M^Cu 



+ istA 




Fig. 490. — The wings of Adelges. (From Patch.) 



HOMOPTERA 415 

Family APHIDID^ 
The Typical Aphids 

To this family belong the far greater ntimber of the genera and 
species of the Aphidoidea. The distinctive characters of this family 
are given under A in the table above. For a detailed discussion of 
the wing-venation of these insects, see Patch ('09). 

In the Aphididce there exists a remarkable type of developrnent 
known as heterogamy or cyclic reproduction. This is characterized 
by an alternation of parthenogenetic generations with a sexual 
generation. And within the series of parthenogenetic generations there 
may be an alternation of winged and wingless forms. In some cases 
the reproductive cycle is an exceedingly complicated one, and differ- 
ent parts of it occur on different species of food plants. 

In those cases where different parts of the reproductive cycle 
occur on different food-plants, the plant on which the over-wintering 
fertilized egg is normally deposited and upon which the stem-mother 
and her immediate progeny develop is termed the primary host; a.nd 
that plant to which the migrants fly and from which a later form in 
the series migrates to the primary host is known as the secondary host. 

Different species of aphids differ greatly in the details of their 
development; it is difficult, therefore, to make generalizations re- 
garding this matter. The following account will serve to indicate the 
sequence of the forms occurring in the reproductive cycle of a migrat- 
ing aphid, one in which the different parts of the cycle occur on 
different food-plants. This account refers to what occurs in the 
North, where the winter interrupts the production of young, and eggs 
are developed which continue the life of the species through the 
inclement season. In hot climates also, where there is a wet and a dry 
season, eggs are produced to carry the species over the period when 
succulent food is lacking. And in some cases in the North, on ex- 
hausted vegetation the non-migratory species produce eggs during 
the summer months. 

The stem-mother.- — In the spring there hatches from an over- 
wintering egg a parthenogenetic, viviparous female, which lives on 
the primar}^ host. As this female is the stock from which the summer 
generations spring, she is known as the stem-mother or fundatrix. 
The stem-mother is winged in some species of one of the tribes 
(Callipterini) ; but usually she is wingless. 

The wingless agamic form. — In most species the stem-mother gives 
birth to young which do not develop wings and which are all 
females. These reproduce parthenogetically and are known as the 
wingless agamic form or spurice aptercc.* These reproduce their kind 
for a variable number of generations and then produce the next form. 
All of these generations live on the primary host. In a few species 
the wingless agamic form rarely appears if at all. 

*Sptiricc (New Latin, fern, pi.); Lat. spurius, an iHegitimate or spurious child. 



416 AN INTRODUCTION TO ENTOMOLOGY 

The winged agamic form. — After a variable number of generations 
of the wingless agamic form have been developed and tiie food-plant 
has become overstocked by them, there appears a generation which 
becomes winged and which migrates to the secondary host. These 
are all parthenogenetic, viviparous females. They are known as the 
winged agamic form or spur ice alatce or migrants or migrantes. In some 
species, the second generation, the offspring of the stem-mother, are 
winged migrants. 

When the migrating winged agamic form becomes established on 
the secondary host, it produces young which are all females of the 
wingless agamic form. After a variable number of generations of 
this form have been developed, there is produced a generation of 
winged agamic females which migrate from the secondary host to 
the primary host. The two forms developed on the secondary host, 
the wingless and the winged agamic forms, may closely resemble the 
corresponding forms previously developed on the primary host or 
may differ markedly from them. 

The members of the last generation of the series of partheno- 
genetic forms, which produce the males and the oviparous females, 
are termed the sexuparce. In some non-migrating species this genera- 
tion is wingless. 

The males and the oviparous females . — The winged agamic females 
that have migrated from the secondary host to the primary one, 
here give birth to true sexual forms, male and female. These pair, 
and each female produces one or more eggs. These are sometimes 
designated as gamogenetic eggs to distinguish them from the so-called 
}va developed in agamic females. See note on page 191. 

The males and the oviparous females are termed collectively the 
sexuales; and some writers refer to the oviparous females as the 
ovipara. (Note that ovtpara is a plural noun.) 

The sexuales differ greatly in form and habits in the different tribes 
of aphids. In the more generalized aphids the ovipara of some species 
are winged, and the males are very commonly winged; both sexes 
have beaks and feed in the same way as do the other forms; and each 
female produces several eggs. In some of the more specialized aphids 
the sexuales are small, wingless, and beakless; consequently they can 
take no food. Each female produces a single egg, which in some cases 
is not deposited but remains throughout the winter within the 
shriveled body of the female. 

In some cases the young produced by the agamic females aie 
each enclosed in a pellicle when born ; this is soon ruptured and the 
young aphid escapes from it. The young thus enclosed are termed 
pseudova by many writers. 

The foregoing account, omitting exceptions and variations, can be 
summarized as follows : 

A. DIFFERENT TYPES OF INDIVIDUALS IN THE APHIDID.E 

First type. — The stem-mother or fundatrix, which is hatched from a fertihzed 
egg, is usually wingless, and reproduces parthenogenetically. 

Second type. — The parthenogenetically produced wingless agamic females. 



HOMOPTERA 417 

Third type.— The parthenogenetically produced winged agamic females. 
Fourth type. — The sexual forms, males and oviparous females. 

B. SEQUENCE OF GENERATIONS IN A MIGRATING SPECIES 

Only the first of a series of similar generations is counted. 

First generation. — The stem-mother. 

Second generation. — Wingless agamic females. There may be a series of 
generations of this form here. 

Third generation. — Winged agamic females. These migrate to the secondary 
host. 

Fourth generation. — -Wingless agamic females. There may be a series of 
generations of this form here. 

Fifth generation. — Winged agamic females. These migrate to the primary 
host and are the sexuparae. 

Sixth generation. — Males and oviparous females. The females produce the 
fertilized eggs from which the stem-mothers are hatched, thus completing the life- 
cycle. 

A remarkable fact that has been demonstrated by several ob- 
servers is that the ntmiber of generations of the wingless agamic 
form may be influenced by the conditions under which the aphids 
live. In an experiment conducted under my direction by Mr. 
Slingerland, in the insectary at Cornell University, we reared 98 
generations of the wingless agamic form without the appearance of 
any other form. The experiment was carried on for four years and 
three months without any apparent change in the fecundity of the 
aphids, and was discontinued owing to the press of other duties. As 
the aphids were kept in a hothouse throughout the winters, seasonal 
influences were practically eliminated ; and as members of each gen- 
eration were placed singly on aphid-free plants and their young re- 
moved as soon as born, there was no crowding. 

In order to determine the influence of crowding, members of the 
sixtieth generation were placed on separate plants and their young 
not removed. At the end of three weeks the winged agamic form ap- 
peared, evidently in response to need of migration to less densely 
populated plants ; while in other cages where the young were removed 
promptly, no migrants appeared up to the end of the experiment. 

The family Aphididse includes a very large number of genera and 
species. The genera are grouped into tribes and these into subfamilies 
in various ways by different authors. Recent classifications by 
American authors are those of Oestlund ('18) and Baker ('20). Four 
subfamilies are recognized by Baker. The characters of these sub- 
families given below are largely compiled from this author. 

Subfamily APHIDIN.E 

To this subfamily belong most of the species of aphids that are 
commonly seen living free {i. e., not in galls) upon the foliage of 
plants. But while most of the species feed on foliage, some of them 
attack stems and roots. Their attacks on foliage in some cases merely 
cause a weakening of it; in other cases, the leaves become curled or 
otherwise distorted; such distortions are termed pseudo galls. True 
galls formed by aphids are described in the accounts of the last two 
subfamilies. 



418 AN INTRODUCTION TO ENTOMOLOGY 

In the Aphidinas the males and the oviparous females are com- 
paratively generalized; they are furnished with functioning mouth- 
parts and feed as do the other forms; the females lay several eggs; 
in a few species the oviparous females are winged ; and winged males 
are common. Wax-glands are not abundant in members of this sub- 
family ; and the antennal sensoria are oval or subcircular. 

The following are a few of the more common representatives of 
the Aphidinse. These are selected to illustrate some of the more 
striking differences in habits exhibited by the different species. 



a. BARK-FEEDING APHIDIN^ 

The following species will serve as an example of the bark -feeding 
species belonging to this subfamily, and also of the maximum size 
reached by any aphid. 

The giant hickory-aphid, Longistigma cdrycB. — This is a very large 
species, one of the largest aphids known, measuring to the tip of the 
abdomen 6 mm., and more than lo mm. to the tips 
of the wings (Fig. 491). It can be distinguished by 
the shape of the stigma of the fore wings, which is 
drawn out at the tip to an acute point extending 
Fig. 491.— LoKgi- aknost to the tip of the wing. The top of the thorax 
s tgma carycB. ^^^ ^-^^ veins of the wings are black and there are 
four rows of little transverse black spots on the back. The body is 
covered with a bluish white substance like the bloom of a plum. 
This is a bark-feeding species; it is found clustered on the under 
side of limbs in summer. It infests hickory^ maple, and several 
other forest trees. The oviparous female is wingless; the male, 
winged. 

b. LEAF-FEEDING APHIDIN^ 

Examples of the leaf-feeding species belonging to this subfamily 
can be found on a great variety of plants. Among those most easily 
observed are the species infesting the leaves of fniit trees, and 
especially the following. 

The apple-leaf aphis. Aphis pomi. — This is a bright green species, 
the entire life-cycle of which is passed on the apple. The migrants 
fly to other parts of the infested tree or to other apple-trees. As a 
result of the attacks of this species the leaves of the apple are often 
badly curled and sometimes drop off the tree. 

The rosy apple-aphis, Anuraphis rdseus. — -The common name of 
this species refers to the fact that the agamic females are usually 
of a pinkish color; but they may vary in color to a light brown, 
slaty gray, or greenish black, with the body covered with a whitish 
coating. This species is most common on apple; but it infests also 
pear, white thorn, and three species of Sorbus. It is a migrating spe- 
cies. 



HOMOPTERA 419 

The appie-bud aphis, Rhopalosiphum pruniJolicB. — This is the 
species that most commonly infests the opening apple-buds, often 
nearly covering them. It also infests pear, plimi, quince, and many 
other plants. It is a migrating species; various species of grain serve 
as its secondary host. 



C. ROOT-FEEDING APHIDIN^ 

The corn-root aphis, Anuraphis maidi-radtcis . — This is a serious 
pest of corn throughout the principal corn-growing States, sometimes 
totally ruining fields of corn. Broom-corn and sorghum are the only 
other cultivated crops injured by it ; but it infests many species of weeds 
that grow in corn-fields. Our knowledge of this species is largely the 
result of investigations of Professor S. A. Forbes, who has published 
several detailed accounts of it in his reports as State Entomologist 
of Illinois. This author found that this aphid is largely dependent 
on a small brown ant, the corn-field ant (Ldsitis americdims), the 
nests of which are common in corn-fields. The ants store the winter 
eggs of the aphids in their nests and care for them throughout the 
winter. In the spring, when the stem-mothers hatch, they are trans- 
ferred by the ants to the roots of the weeds upon which they feed. 
As soon as corn-plants are available, the ants transfer the aphids to 
the roots of the corn, the ants digging burrows along the roots of the 
corn for this purpose. The ants in return for their labors derive 
honey-dew from the aphids. 

One can understand how these ants that attend aphids that are 
excreting honey -dew should learn to drive away the enemies of the 
aphids, as is often done ; but is it not wonderful that Lasius americanus 
should recognize the importance of preserving the eggs from which 
their herds are to develop ! 

The strawberr}^-root aphid, Aphis forhesi. — The winter eggs of this 
species are found upon the stems and along the midribs of the green 
leaves of strawberry plants. The stem-mothers and one or more 
generations of the offspring feed upon the leaves in the early spring. 
But a little later in the season the corn-field ant appears and transfers 
the aphids to the roots of the strawberry, where it cares for them in 
the same way that in corn-fields it cares for the corn-root aphis. 
This ant is entirely responsible for the infesting of the roots by the 
aphids; and it is here that the greatest injury to the plants is done. 



Subfamily AIINDARIN^ 

This subfamily was established by Baker ('20) for the reception 
of the genus Mindarus, which can be distinguished from all other 
living aphids by the venation of the wings. In this genus the radial 
sector of the fore wings separates from vein R^ at the base of the 



420 



AN INTRODUCTION TO ENTOMOLOGY 




long, narrow stig- 
ma (Fig. 492). In all 
other living aphids 
the origin of the ra- 
dial sector is much 
nearer the tip of the 
wing; but in many 
of the fossil aphid 
wings it is as in 
Mindarus . The 
males and the 
oviparous females 
are small and wing- 
less; but they retain the beak, at least in most individuals, and feed. 
The female lays several eggs. 

Only one species, Mindarus ahietinus, is known. This lives free 
upon the twigs of spruce and other conifers, which become somewhat 
distorted and are often killed by the attack of the insects. When 
disturbed this insect secretes large quantities of honeydew. 

The life-cycle of this species usually includes only three genera- 
tions, the stem-mother, the winged agamic females {sexuparce), and 
the sexual forms. Sometimes there is a generation of wingless 
agamic females. 

This species was redescribed by Thomas as Schizoneura pinicola. 



Fig. 492. — Wings of Mindarus. (After Patch.) 



Subfamily ERIOSOMATIN^ 

This subfamily includes those genera of aphids in which the males 
and the oviparous females are greatly specialized by reduction. They 
do not have functioning mouth-parts; some have a beak when born 
but lose it at the first molting; in others the beak is vestigial at birth. 
As they cannot feed, they remain small. Both sexes are wingless. 
The oviparous females produce each a single egg, which in some 
species is not laid but remains throughout the winter in the shriveled 
body of the female. 

In this subfamily, the cornicles are much reduced or are wanting ; 
wax-glands are abundantly developed; and the antennal sensoria are 
prominent. These are often annular. 

The members of this subfamily that are most likely to attract 
attention can be grouped under two heads: a, the woolly aphids; 
and b, the gall-making Erisomatinse. These groups, however, do not 
represent natural divisions of the subfamily and do not include all 
members of it. They are merely used for convenience in the present 
discussion. 

a. THE WOOLLY APHIDS 



The woolly aphids are the most conspicuous members of the 
Aphididae, on account of the abundant, white, waxy excretion that 



HOMOPTERA 421 

covers colonies of them. The three following species are widely dis- 
tributed and are common. 

The woolly apple aphis, Eriosdnia lamgera. — This plant-louse, on 
account of its woolly covering and the fact that it is a serious pest of 
the apple, is known as the woolly apple aphis, although the apple is 
its secondary host. This insect not only has a complicated series of 
generations but the life-cycle is subject to variations ; its usual course 
is as follows : 

The winter-eggs are deposited in crevices of the bark of elm. 
From these eggs stem-mothers hatch in the spring and pass to the 
young leaves, where they produce either the well-known leaf-curl of 
the ekn or, when a group of terminal leaves are affected, what has 
been termed a rosette, which is a cluster of deformed leaves. Within 
these pseudogalls the second generation is produced ; this consists of 
vv^ingless agamic females. The offspring of these, the third generation, 
become winged and migrate from the elm to the apple. Here they 
produce the fourth generation, the members of which live on the 
water-shoots or the tender bark of the apple, and are wingless. The 
fifth generation also consists of wingless agamic females. Some of 
these develop on the bark of the branches, which apparently ceases 
to grow at the point of attack but swells into a large ridge about the 
cluster of plant-lice, leaving them in a sheltered pit ; the aphids also 
frequently congregate in the axils of the leaves and the forks of the 
branches. Other members of this generation pass to the roots of the 
tree, where they produce knotty swellings on the fibrous roots. The 
sixth generation consists, in part, of winged agamic females which 
migrate from the apple to the elm, where they produce the seventh 
generation. This generation, the last in the series, consists of the 
males and oviparous females, both of which are beakless and wing- 
less. These pair and each female produces a single egg, which is 
found in a crevice of the bark with the remains of the body of the 
female. 

The course of events outlined above may be modified in two ways : 
first, it is said that the sexual forms are sometimes produced on the 
apple; and second, some members of the sixth generation do not 
develop wings and migrate, but are wingless and produce young that 
hibernate on the apple. This species infests also mountain ash and 
hawthorn, as secondary hosts. 

The elm-feeding generations of this species that cause the leaf- 
curls and rosettes have been known as Schizoneura americdna. And 
there are also found during the summer aphids on tender elm bark 
which are believed to belong to this species and which have been 
described under the name Schizoneura rileyi. In the Pacific Coast 
States there is another species of aphid that produces leaf curl on elm. 
This is Schizoneura ulmi, a European species, which in Europe has 
been found to migrate to Ribes. 

The alder-blight, Proctphilus tesselldtus. — ^A woolly aphid that is 
found in dense masses on the branches o£ several species of alder is 
known as the alder-blight. Colonies of this species are easily found 



422 AN INTRODUCTION TO ENTOMOLOGY 

in the regions where it occurs, as their covering of flocculent excretion 
renders them very conspicuous. These colonies are of especial in- 
terest, as within them is found the predacious larva of the wanderer 
butterfly, Feniseca tarquiniiis, which feeds on the aphids. 

In the late stunmer or early autumn the last generation of wingless 
agamic females bring forth young, which winter among the fallen 
leaves at the base of the alder and return to the branches in the 
spring. From this there appears to be no need of an alternate host. 
But it was found by Dr. Patch that at the same time that the form 
that hibernates at the base of the alder is produced, winged migrants 
appear and fly to maple trees, where they give birth, in the crevices 
and rough places in the bark, to males and oviparous females. Each 
of these females produces a single egg. From these eggs there hatch in 
the spring aphids which pass to the lower side of the leaves of the 
maple, where they become conspicuous on accotmt of their abundant 
and long woolly excretion. In this period of its existence this species 
is the well-known pest of the maple that has long been known as 
Pemphigus acerjdlii, which name must now be regarded as a synon^mi 
of Proctphilus tesselldtus, the older name. In July winged migrants 
are developed on maple which fly to alder. 

The alder-blight excretes honeydew abundantly; the result is 
that the branches infested by this insect, and those beneath the cluster 
of aphids, become blackened with fungi that grow upon this excretion. 
There is also a curious fungus which grows in large spongy masses 
immediately beneath the cluster of plant-lice; this is known to bot- 
anists asScorias spongiosa. It is evidently fed by the honeydew that 
falls upon it. 

The beech-tree blight, Prociphilus imbricdtor . — This infests both 
twigs and leaves of beech. Lilce the preceding species it occurs in 
clusters of individuals, each of which is clothed with a conspicuous 
downy excretion. These clusters often attract attention by the 
curious habit which the insects have of waving their bodies up and 
down when disturbed. When an infested limb is jarred, the aphids 
emit a shower of honeydew. Owing to the abundance of this excretion, 
the branches and leaves of an infested tree become blackened by 
growths of fungi, as with the preceding species. The life-cycle of this 
species has not been determined. 

h. THE GALL-MAKING ERIOSOMATIN^ 

Certain members of this subfamily cause the growth of remarkable 
galls, resembling in this respect certain members of the following 
subfamily. Among the gall-making Eriosomatinee that are most likely 
to attract attention are the following. 

The cockscomb elm-gall colopha, Colopha ulmtcola. — There are 
two species of aphids that make similar galls on the leaves of elm. 
These galls are commonly known as cockscomb ekn -galls on account 
of their shape. Those made by the two species of aphids are so 
similar that a description of one will apply to the other. In each case 



HO MOP T ERA 



423 



the gall is an excrescence resembling a cock's conib in form, which 
rises abruptly from the upper surface of the leaf (Fig. 493, a). It is 
compressed, and has its sides wrinkled perpendicularly and its summit 
irregularly gashed and toothed. It opens on the under side of the 
leaf by a long slit-like orifice. 

The winter eggs can be found during the winter in the crevices 
of the bark of the elm; each egg is usually enclosed in the dry skin 
of the oviparous female (Fig. 493, h). In the spring the stem-mothers 



^^=p=F^ 




Fig. 493. — Colopha ulmicola: a, leaf showing galls from above and beneath; b, 
fertilized egg surrounded by the skin of the female; c, newly born young of the 
second generation; h, its antenna; d, full-grown nymph of the second genera- 
tion; e, adult of second generation; /, antenna of migrant ; g, antenna of stem- 
mother. (From Riley.) 



pass to the leaves and each causes by its attack the growth of a gall. 
The second generation is produced within the gall; it consists of 
winged agamic females (Fig. 493, e). These migrants can be dis- 
tinguished from those of the other cockscomb elm-gall aphid by the 
fact that in this species vein M of the fore wings is forked. 

The migrants of this species pass from the elm to certain grasses, 
among them species of Eragrostis and Panicum. The forms found on 
these secondary hosts have been described under the name Colopha 
eragrostidis, but this is a much later name than Colopha ulmtcola. 



424 



AN INTRODUCTION TO ENTOMOLOGY 



The cockscomb elm-gall tetraneura, Tetraneura gramlnis. — The 
life-cycle of this species is quite similar to that of the preceding one. 
The primary host is elm. The stem-mothers cause the growth of 
cockscomb-like galls; and the migrants produced in these galls pass 
to grasses. These migrants differ from those of the preceding species 
in that vein M of the fore wings is not forked. This species was first 

described from individu- 
als found on the second- 
ary hosts and was named 
Tetraneura gramlnis . Lat- 
er, forms found on elms 
were named Tetraneura 
colophoides . 

For a detailed ac- 
count of the gall-aphids 
of the elm, see Patch 
Cio). 

The poplar-leaf gall- 
aphid, Thecdhius populi- 
caulis. — This aphid is 
common on several spe- 
cies of poplar. It makes 
a swelling the size of a 
small marble on the leaf 
at the junction of the 
petiole with the blade. 
This gall is of a reddish 
tint, and has on one side 
a slit-like opening. In the early part of the season each gall is occu- 
pied by a single wingless female, probably the agamic stem-mother, 
which by midsummer becomes the mother of niunerous progeny. 
These are winged and probably migrate to some other host-plant; 
but the life-cycle of this species has not been determined. 

The vagabond gall-aphid, Mordwilkoja vagabunda.- — This species 
infests the tips of the twigs of several species of poplar; here it causes 
the growth of large corrugated galls, which resemble somewhat the 
flower of the double cockscomb of our gardens. The galls are at first 
bright green, but later turn black, become woody, and remain on the 
trees during the winter (Fig. 494). Very little is known regarding the 
life-cycle of this species. 




Fig. 494. — The vagabond i)oplar-gall. 
Walsh and Riley.) 



(From 



Subfamily HORMAPHIDIN^ 



The members of this subfamily are usually gall-makers, resembling 
in this respect certain members of the Eriosomatinse, and also re- 
sembling them in that the antennal sensoria are annular. But in 
this subfamily the sexual forms are not so specialized by reduction 
as in the preceding one. In the Hormaphidinffi, although the males 
and the oviparous females are small and wingless, they possess 



HOMOPTERA 



425 



beaks, they feed, and the oviparous female lays more than one egg. 
In this subfamily great specialization of wax-producing organs occurs. 
In many species some of the agamic generations become greatly modi- 
fied in form so that they do not resemble the more typical aphids. 
In some species these modified forms have the appearance of an 
Aleyrodes; in other species, that of a coccid. 

Our best-known representatives of this subfamily are two species 
of gall-makers, each of which infests alternately witch-hazel and 
birch. The life-histories of these were ver\' carefullv worked out bv 




Fig. 495. — The witch-hazel cone-gall: a, natural size; b, section of gall, enlarged. 
(From Pergande.) 

Pergande ('01); the followini:: accounts are greatly condensed from 
that author. 

The witch-hazel cone-gall aphid, Hormaphis hamamelidis. — The 
winter-egg is deposited on the branches and twigs of witch-hazel 
and hatches early in the spring. The stem -mother, which hatches 
from this egg, attacks the lower surface of the leaf, causing the growth 
of a conical gall on the upper surface of the leaf with a mouth on 
the lower surface (Fig. 495). The second generation, the offspring 
of the stem-mother, consists of many individuals; these are pro- 
duced within the gall, which becomes crowded with them. These 
are agamic females, which become winged, leave the gall, and mi- 
grate to birches, where they deposit their young on the lower side 
of the leaves. The first instar of the third generation, the offspring 
of the migrants, is broadly oval, with the entire margin of the body 



42G 



AN INTRODUCTION TO ENTOMOLOGY 



studded with short and stout excretory tubercles (Fig. 496); from 
each of these there issues a short, glassy, beautifully iridescent, waxy 
rod. The second and third instars of this generation are marked by 

a reduction of the antennae, 
beak, and legs. The fourth 
instar, which is found about 
the middle of June, is aley- 
rodiform (Fig. 497). The 
fourth and fifth generations 
resemble the third, there be- 
ing three aleyrodiform gen- 
erations. The members of 
the sixth generation become 
winged and are the return 
migrants. These fly to 
witch-hazel, where they give 
birth to the seventh genera- 
tion, which consists of males 
and oviparous females. 
These pair and the females 
lay the winter eggs; each 
female produces from five 
to ten eggs. The males and 
In this species the antenna 




Fig. 496.^ — Hormaphis hamamelidis , first instar 
of the third generation. (From Pergande.) 



the oviparous females are both wingless. 
of the winged forms are three-jointed. 

Later experiments by Alorgan and Shull ('10) indicate that this 
species can complete its life-cycle on 
the witch-hazel. According to these ,,r"',-T7 

authors there are only three genera- , "^ ''■"",' '"*'''- /, 

tions; first, the stem-mother, which 
causes the growth of the cone-gall; 
second, the winged forms, which are 
developed in the gall and which spread 
to the leaves ; and third, the males and 
oviparous females. No aleyrodiform 
individuals were found on the witch- 
hazel. 

The spiny witch-hazel-gall aphid, 
Hamameltstes spinosus.— The winter 
eggs of this species are commonly de- 
posited near the flower-buds of witch- 
hazel, late in June or early in July, 
but they do not hatch till May or 
June of the following year. The 
stem-mother attacks the flower-bud. 

which becomes transformed into a large gall of the form shown in 
Figure 498. Within this gall the stem-mother produces the second 
generation; these crowd the gall and develop into winged migrants, 
which leave the gall, from July to late fall, and fly to birches. The 




Fig. 497. — Hormaphis hamamel- 
idis, foiirth instar of the third 
generation. (After Pergande.) 



HOMOPTERA 



427 



young of the migrants, the third generation, feed a short time and 
then settle close to the leaf-buds, where they hibernate; the last in- 




Fig. 498. — The spiny witch-hazel gall: a, mature gall; b, section of gall. (From 
Pergande.) 

star of this generation resembles a coccid (Fig. 499). The fourth 
generation is produced early in the spring ; the young of this genera- 
tion move to the young and tender leaves of the birch, which, as a 





Fig. 499- — Hamamelistes spinosus, last instar of the third generation, much 
enlarged: a, dorsal view; b, lateral view; c, ventral view; d, antenna; <5 
/, g, legs. (From Pergande.) 

result of the attack, become corrugated, the upper surface bulging 
out between the veins, and the folds closing up below. In these 



428 



AN INTRODUCTION TO ENTOMOLOGY 



pseudogalls the fifth generation is produced; the members of this 
generation become winged and migrate to witch-hazel in early 
summer, where they produce the seventh and last generation of the 
series, the males and oviparous females. These pair and the females 
soon lay their eggs. Both sexes are wingless. The winged migrants 
of this species can be distinguished from those of the preceding 
species by their five-jointed antennae 



Family PHYLLOXERID^ 

The Adelgids and the Phylloxerids 

The members of this family differ from the typical aphids in that 
both the sexually perfect females and the parthenogenetic forms lay 
eggs, in lacking vein Ri of the fore wings, and in that the outer part 
of the stigma is bounded behind by the radial sector (Fig. 500). 



Sc.-R^M^Cu^li^-^ g^ 




Fig. 500. — Wings of Adelges. (From Patch.) 

In this family the cornicles are always wanting; and the males and 
sexually perfect females are dwarfed and wingless. 

This family includes two subfamilies, which can be separated by 
the following table. These subfamilies are regarded as distinct 
families by some writers. 



A. The wingless agamic females excrete a waxy flocculence. The winged forms 
have five-jointed antennae, the last three segments of which bear each a single 
sensorium. The wings are held roof-like when at rest. The free part of vein 
Cu of the fore wings is separate from vein 1st A (Fig. 500). The sexual forms 
have a beak. The alimentary canal is normal, producing a fluid excrement. 
The species infest only conifers Adelgin^ 

AA. The wingless agamic females do not secrete a waxy flocculence, but in the 
genus Phylloxerina they excrete a waxy powder. The winged forms have 
three-jointed antenna, the second segment of which bears two sensoria. The 
wings when at rest are laid flat upon the abdomen. The free parts of veins Cu 



HOMOPTERA 



429 



and 1st A of the fore wings coalesce at base (Fig. 501). The sexual forms 

have no beak. The anus is closed. The species do not infest conifers 

Phylloxerin^ 



Sc+lt+Jf+Cif + IsfA 




Fig. 501 . — Wings of Phylloxera. (From Patch.) 

Subfamily ADELGINvE 
The Adelgids 

This subfamily includes those insects found on conifers that have 
been quite generally known under the generic name Chermes. But it 
has been determined that this name should be applied to certain 
jumping plant-lice of the family Chermidce, formerly known as the 
Psyllidae. The necessity of this change is very unfortunate, as much 
has been published regarding members of the Adelginae and in most 
of these accounts they are described under the name Chermes. 

All the species of this subfamily infest conifers; and in all cases 
in which the sexual generation is known, this generation lives on 
spruce. The secondary host may be either larch, pine, or fir. 

Much has been written regarding the life-histories of these insects. 
It has been found that what may be regarded as the t^'pical life-cycle 
of an Adelges or ''Chermes' is a very complex one, including the 
developing of two parallel series of forms differing in habits ; that in 
one of these series a single host-plant, spruce, is infested and the life- 
cycle is completed in one year; while in the other series the life-cycle 
extends over two years and is passed in part upon spruce and in 
part upon larch or some other host-plant. 

In this typical life-cycle, beginning with the individual that 
hatches from a fertilized egg, there are developed five generations, 
the members of which differ in either form or habits or both from 
those of the other generations, before the cycle is completed by the 
production again of fertilized eggs. The actual number of generations 
may be greater than this, owing to the fact that in a part of the cycle 
there may be a series of similar generations only the first of which is 
counted in this enumeration. 



430 AN INTRODUCTION TO ENTOMOLOGY 

This indicating of a typical life-cycle is an effort to outline as 
simply as possible the life-history of these insects. In some species 
it is much more complicated; thus, for example, Borner ('08) in his 
account of the life-history of Cnaphalodes strohildhius recognizes seven 
parallel series of forms. 

The distinctive characters of the five differing generations in the 
typical life-cycle are indicated below. 

A. GENERATIONS ON SPRUCE (Picea) 

A one-year cycle or the first year of a two-year cycle. 

First generation. — This consists of the true stem-mother {fimdatrix vera), 
a wingless agamic female. In the case of those supposed parthenogenetic species 
vvhich do not migrate to another host-plant and which complete their life-cycle in 
one year, this form is the offspring of the second generation, an agamic fortn; 
in the case of species that migrate to a secondary host-plant, and where there are 
two parallel series, the stem-mother is the offspring of either the second generation 
or the fifth generation, the sexual forms. 

The stem-mothers hatch in the autumn; they hibernate immature in crevices 
at the bases of buds, complete their growth in the spring, and by their attack upon 
the buds cause the beginning of the growth of galls. Each stem-mother lays a 
large number of eggs. 

Second generation. — The members of this generation hatch from the eggs laid 
by the stem-mothers, and by their attack upon the buds cause the completion of 
the growth of the galls. The galls are formed by the hypertrophy and coalescence 
of the spruce-needles. The members of this generation have been termed the 
gallicolce, because they inhabit the galls. They reach the last nymphal instar 
within the galls. When this stage is reached, the galls open and the nymphs 
emerge and soon molt, becoming winged agamic females. 

As to their habits, there are two types of gallicolae: first, the non-migrants, 
which remain on the spruce and lay the eggs from which the stem-mothers of the 
one-year cycle are hatched; and second, the migrants, which fly to a secondary 
host-plant, which is not spruce, and where they lay many eggs, but not so many as 
are laid by the stem-mothers. 

B. GENERATIONS ON A SECONDARY HOST 

Part of the second year of a two-year cycle. 

The secondary host may be a species of either larch {Larix), pine (Pinus), 
or fir (Abies); but no galls are produced on any of these. 

Third generation. — The members of this generation hatch from eggs laid by 
migrants of the second generation that have flown from spruce to larch or other 
secondary host and laid their eggs there. The young that hatch from these eggs 
hibernate in crevices in the bark and complete their growth in the spring, becom- 
ing wingless agamic females. The members of this generation and of similar 
generations which follow immediately but which are not numbered here, are 
termed colonici, because they are settlers in a new region, or exsides, that is, 
exiles. Some writers term the first of this series of generations false stem-mothers 
{fundatrices spiirice) to distinguish them from the true stem-mother, which is the 
beginning of the two-year cycle. The members of the third generation resemble 
those of the first generation, but usually lay fewer eggs and do not cause the 
growth of galls. 

The offspring of the third generation are all wingless agamic females, which 
reproduce their kind. Of these there may be a series of generations, which are not 
numbered in this generalized statement; and there may be among these several 
parallel series of generations, differing in the life-cycle but all reproducing 
parthenogenetically on the secondary host. The secondary host may be thus 
infested throughout the year; while the primary host, if there is not an annua] 
series, will be free during the interval between the migration of the second genera- 
tion and the return migration of the fourth generation. 



HO MO PT ERA 431 

Among the offspring of the third generation two types are recognized by 
^larchal ('13): first, nymphs which remain undeveloped for a time, the sistens 
type; and second, nymphs which develop at once into wingless agamic females, 
the progrediens type.* 

Fourth generation. — The members of this generation are produced by indi- 
viduals of the progrediens type of the third generation. They develop into winged 
agamic females. The adults migrate to spruce and there lay a small number of 
eggs. Since their offspring are the sexual forms, this generation is known as the 
sexuparcB. 

C. A GENERATION ON SPRUCE 

The completion of the second year of a two-year cycle. 

Fifth generation. — From eggs laid by the sexuparas that have migrated from 
the secondary host to spruce, there are developed males and sexually perfect 
females, termed the sexuales; both of these forms are wingless. They pair and 
each female lays a single egg. These eggs hatch in the autumn; the young 
hibernate and become the true stem-mothers. Thus is completed the two- 
year life-cycle. 

Omitting the annual series, the typical two-year life-cycle includes the follow- 
ing series of generations, which are described above. 

First. — The wingless agamic stem-mother. 

Second. — The winged agamic migrants. 

Third. — The wingless agamic colonici or exsules. 

(a) The sistentes, several generations. 

(b) The progredientes, several generations. 
Fourth. — The winged agamic sexuparae. 

Fifth. — The wingless sexuales, males and sexually perfect females. Each 
female produces a single fertilized egg, from which hatches a stem-mother, thus 
completing the life-cycle. 

In the case of some species, which have been studied very carefully 
by different observers, only an annual series, consisting of the first 
and second generations described above, is known. It should be 
noted that in a lif e-c>xle of this kind there are no sexual forms and that 
although a winged form appears it is not known to migrate. These 
facts indicate that either some members of the winged generation 
migrate to a secondary host-plant which has not been discovered, or 
that the species in question have become, by adaptation, purely par- 
thenogenetic. Which of these alternatives is true has been much dis- 
cussed. 

The following species are some of the more common of our repre- 
sentatives of this subfamily. 

The pine-leaf adelges, Adelges pinijolice. — Our knowledge of the 
life-history of this species is still fragmentar>^ In one part of its life- 
cycle it infests the leaves of white pine {Pinus strobus). The genera- 
tions found here are winged agamic females. These attach them- 
selves firmly to the pine-needles, each with its head directed towards 
the base of the needle. Within each there are developed about one 
hundred eggs, which are not extruded. After the death of the female, 
the mass of eggs remains adhering to the leaf, covered over and 



"Sistens, Latin sisto, to stand; progrediens, Latin pro, forth, gradior, to go. 



432 



AN INTRODUCTION TO ENTOMOLOGY 




g. 502. — Gall of Adelges 
pinifolicB on spruce. 



protected by the remains of the body and closed wings of the dead 
insect. 

It has been determined that these plant- 
lice infesting the pine leaves are specifically 
identical with those that issue from a cone- 
like gall found on several species of spruce 
(Fig. 502). The spruce-inhabiting form has 
been known as Chermes abieticolens; but 
-piniJolicB is the older specific namo and 
should be used for all forms of this species. 
It is probable that this species has a two- 
year life-cycle and that spruce is its primary 
host and pine its secondary host. 

The green-winged adelges, Adelges ahle- 
tis. — This species causes the growth of pine- 
apple-shaped galls on several species of 
spruce (Fig. 503). It is a European species 

and its life-history has been the subject of m.uch controversy. It is 
held by Borner ('08) that it has a typical life-cycle in which there are 
two parallel series: first, an annual series on spruce alone; and 
second, a two-year series in which larch is 
used as a secondary host. On the other 
hand, Cholodkovsky ('15) maintains that it 
is a parthenogenetic species; that its life- 
cycle includes only two generations, the 
agamic hibernating stem-mothers and the 
gallicolae; and that the form with a typical 
life-cycle is a distinct species {Chermes 
viridis). Dr. Patch ('09) has studied Adel- 
ges abietis in Maine and has found only the 
parthenogenetic forms, the hibernating stem- 
mothers and the gallicolse; thus confirming 
the conclusion that it may have become a 
parthenogenetic species. 

The pine-bark adelges, Adelges pinicorti- 
cis. — This species infests several species of 
pine, but especially white pine. The trunks 
and larger limbs of the infested trees often 
-Gall of Adelges ^PPff^ ^^ '^ whitewashed; this is due to the 
woolly excretion which covers the bodies 01 
the insects. But little is known regarding the 
life-cycle of the species. Wingless females, which are doubtless agamic 
as they lay many eggs, hibernate on the pine and feed on the bark 
in the spring. They lay their eggs in April; these soon hatch and the 
young develop into winged agamic females in May. These soon dis- 
appear and the pine is said to be free from the pest during the simimer. 
Return migrants to the pine have not been observed; but there 
must be a generation of these, the parents of the wingless hibernating 




Fig. 503-- 
ahietis. 



no MO PT ERA 433 

generation, if, as stated, the pines are free from the pest during the 
summer. 

Subfamily PHYLLOXERIN^ 

The Phylloxerids 

The distinguishing characters of this subfamily are given under 
AA in the table on page 428 and need not be repeated here. It in- 
cludes two genera, Phylloxera and Phylloxerina. 

The genus Phylloxerina is distinguished by the fact that the 
wingless agamic females excrete a waxy powder, which gives them 
the appearance of mealy-bugs. Species of this genus have been found 
in this countn^ on poplar, willow, and sour-gum. 

The genus Phylloxera is represented by the grape Phylloxera and 
thirty or more described species that infest forest-trees — hickory, 
oak, and cnestnut. Most of these are found on hickory. Those 
on hickory cause the growth of galls either on the leaves or on the 
tender twigs and petioles. Other species produce either pseudogalls 
or white or yellowish circular spots on the infested leaves. The species 
infesting forest -trees were monographed by Pergande ('04). 

Although in this subfamily there is a generation of winged mi- 
grants in the life-cycle of each species, few if any of them have a 
secondary host. The migrants fly to other parts of the infested plant 
or to other plants of the same species. 

So far as is known, the life-c3-cle of the species infesting forest-trees 
is a comparatively simple one. The stem-mother hatches in the 
spring from an over-wintering, fertilized egg and causes the growth of 
a gall; she develops within the gall and produces unfertilized eggs. 
From these eggs hatch young that develop into winged agamic 
females. These produce eggs of two sizes; from the smaller eggs 
hatch males; and from the larger ones, females. The sexes pair and 
each female lays a single fertilized egg. In some species these eggs 
are laid in June and do not hatch till the following April. 

The grape Phylloxera, Phylloxera vastdtrix. — From an economic 
standpoint this species is the most important member of the Phyl- 
loxerinse; millions of acres of vineyards have been destroyed by it.* 
The most extensive ravages of this pest have occurred in France 
and in California. This species is a native of the eastern United 
States, where it infests various species of wild grapes. It does not 
injure these seriously; but when it was introduced into France it 
was found that the European grape, Vitis vinifera, is extremely sus- 
ceptible to its attack. The great injury to the vineyards of California 
is due to the fact that it is the European grape that is chiefly grown 
there. 

The presence of this insect is manifested by the infested vines 
in two ways: first, in the case of certain species of grapes, there 

*"The Phylloxera when at its worst had destroyed in France some 2,500,000 
acres of vineyards, representing an annual loss in wine products of the value of 
150,000,000." (Marlatt '98.) 



434 



AN INTRODUCTION TO ENTOMOLOGY 




^>^# 



Fig. 504. — Leaf of grapewith galls of Phylloxera. 
(From Riley.) 



appear upon the lower surface of the leaves galls, which are more or 
less wrinkled and hairy (Fig. 504), which open upon the upper surface 

of the leaf, and each of 
which contains a wingless, 
agamic plant-louse and her 
eggs; second, when the fi- 
brous roots of a sickly vine 
are examined, we find, if the 
disease is due to this insect, 
that the minute fibers have 
become swollen and knotty; 
or, if the disease is far ad- 
vanced, they may be en- 
tirely decayed (Fig. 505, c). 
Upon these root-swellings 
there may be found wing- 
less, agamic, egg-laying 
plant-lice, the authors of 
the mischief. 

The life-history of this 
species is a complicated one, 
due to the fact that parallel 
series of generations with 
different life-cycles may be developed at the same time. While a 
fertilized winter egg may be considered a part of the typical life-cycle, 
some of the agamic females hibernate on the roots of the vine and 
form a part of a series of agamic generations that apparently may 
continue indefinitely year after year. 

The typical life-cycle, that one in which males and sexually 
perfect females form a part, extends over two years and includes 
four forms as follows : 

The gallicolcB. — From an over-wintering fertilized egg, there hatches 
in the spring a wingless agamic stem-mother, which passes to a leaf 
and by her attack causes the growth of a gall, within which she passes 
the remainder of her life. She reaches maturity in about fifteen 
days, fills the gall with eggs, and soon dies. The young that hatch 
from the eggs laid by the stem-mother resemble her in being wingless 
agamic females; they escape from the gall, spread over the leaves, and 
in turn cause the growth of galls. Six or seven generations of this 
form (Fig. 506) are developed during the simimer. They are termed 
the gallicolcs. 

The radicicolce or colonici. — On the appearance of cold weather, 
young hatched from eggs laid by the gall-inhabiting form pass down 
the vines to the roots, where they hibernate. This completes the 
first year of the two-year cycle. In the following spring these colonici, 
that is, settlers in a new region, attack the fibrous roots, and cause 
the growth of knotty swellings on them (Fig. 505, b, c) and ultimately 
their destruction. This is the most serious injury to the vine caused 
by this species. There is a series of generations of the root-inhabiting 



HO MOP T ERA 



435 



form all of which are wingless agamic females. This form (Fig. 507) 
differs somewhat in appearance from the gallicolae. 

The migrants or sexuparcB.- — -During the late summer and fall there 
are hatched from eggs laid by some individuals of the root-inhabiting 




Fig. 505. — Phylloxera, root-inhabiting form: a, shows a healthy root; b, one on 
which the hce are working, representing the knots and swellings caused by 
their punctures; c, a root that has been deserted by them, and where the rootlets 
have commenced to decay; d, d, d, show how the lice are found on the larger 
roots; e, agamic female nymph, dorsal view; /, same, ventral view; g, winged 
agamic female, dorsal view; h, same, ventral view; i, magnified antenna of 
winged insect; j, side view of the wingless agamic female, laying eggs on roots; 
k, shows how the punctures of the lice cause the large roots to rot. (From 
Riley.) 

form, young that develop into winged agamic females (Fig. 505, g, h). 
These come forth from the ground, fly to neighboring vines, and 
lay eggs in cracks in the bark or under loose bark. They lay only a 
few eggs, from three to eight. 



436 



A IS INTRODUCTION TO ENTOMOLOGY 




Fig. 506. — Phylloxera, gall-inhabiting form: a, b, 
newly hatched nymph, ventral and dorsal views ; c, 
egg ; d, section of gall ; e, swelling of tendril ; /, g, 
h, mother gall-louse, lateral, dorsal, and ventral 
views; i, her antenna; j, her two-jointed tarsus. 
Natural sizes indicated at sides. (From Riley.) 



The sexuales. — 
The eggs laid by the 
winged migrants are 
of two sizes ; from the 
smaller eggs there 
hatch males ; and 
from the larger eggs, 
sexually perfect fe- 
males. These pair 
and each female pro- 
duces a single egg, 
which is laid in the fall 
on old wood. Here it 
remains over winter, 
and from it in the fol- 
lowing spring a stem- 
mother is hatched. 
This completes the 
two-year life-cycle. 

Control.- — Owing 
to the great injury 
that this species has 
done to vineyards, 
hundreds of memoirs have been published regarding it; but, as yet, 
no satisfactory means of 
destroying it that can be 
generally used has been 
discovered. Where the 
soil conditions are favor- 
able it can be destroyed 
by the use of carbon-bi- 
sulphide, but this is an 
expensive method ; where 
the vineyards are so situ- 
ated that they can be 
submerged with water at 
certain seasons of the 
year, the insect can be 
drowned ; and it has been 
found that vines growing 
in very sandy soil are less 
liable to be seriously in- 
jured by this pest. 

While it is usually im- 
practicable to destroy 
this pest in an infested 
vineyard, there is a pre- 
ventative measure that 
has given good results. 




Fig. 507. — Phylloxera, root-inhabiting form: a, 
roots of Clinton vine showing the relation of 
swellings to leaf -galls, and power of resisting de- 
composition; b, nymph as it appears when 
hibernating; c, d, antenna and leg of same; e, 
f, g, forms of more mature lice; h, granulations 
of skin; i, tubercle; j, transverse folds at 
border of joints; k, simple eyes. (From Riley.) 



HOMOP TERA 



437 



Certain varieties of American grapes are not seriously injured by the 
root-form of the Phylloxera. By growing these varieties, or by using 
the roots of them as stocks on which to graft the susceptible European 
varieties, the danger of injur^^ by this pest is greatl}' reduced. 




Fig. 509. 
besii. 



-Aleurochiton for- 



Family ALEYRODID^ 
The Aleyrodids or White Flies 

The members of this family are small or minute insects ; our more 

common species have a wing-expanse of about 3 mm. In the adult 

state both sexes have four wings, differing in this respect from the 

Coccidag, with which they were classed by the early entomologists. 

The wings are transparent, white, clouded or mottled with spots or 

bands. The wings, 

and the body as well, 

are covered with a 

whitish powder. It is 

this character that 

suggested the name of 

the typical genus,* 

and the common name 

white flies. 

In the immature 

stages, these insects Fig- 508. — Analeyrodid 

are scale-like in form 

and often resemble somewhat certain species of the genus Lecanium 

of the family Coccidas. Except during the first stadium, the larvae 

remain quiescent upon the 
leaves of the infested plant 
and in most species are sur- 
rounded or covered by a 
waxy excretion. In Figure 
508 there is represented one 
of the many forms of this 
excretion. Here it consists 
of parallel fibers, which ra- 
diate from the margin of the 
body, and its white color 
contrasts strongly with the 
dark color of the insect. In 
some species the fringe of 
excretion is wanting; and 
in others, the excretion from 
the margin of the body, in- 
stead of extending laterally 
and forming a fringe, is di- 
rected toward the leaf upon 
which the insect rests, and 




Fig. 510. — Wings of Udamoselis. (After En- 
derlein, with changed lettering.) 



*Aleyrodes (a\evpd)8r]s), like flour. 



438 AN INTRODUCTION TO ENTOMOLOGY 

thus the body is Hfted away from the leaf and is perched upon an 
exquisite pahsade of white wax (Fig. 509). 

The members of this family feed exclusively on the leaves of the 
host-plants. With few exceptions they are not of economic impor- 
tance ; and also with few exceptions, the injurious species are not wide- 
ly distributed over the world as are many aphids and coccids. This is 
probably due to the fact that as they live exclusively on leaves they 
are not so liable to be transported on cuttings and nursery stock. 
They are most abundant in tropical and semi-tropical regions. 

The adults present the following characters : The compound eyes 
are usually constricted in the middle and in some species each eye 
is completely divided. In some cases the facets of the two parts of a 
divided eye are different in size ; it is probable that in such cases one 
part is a day-eye and the other part a night-eye (see page 1 44) . The 
ocelli are two in number; each ocellus is situated near the anterior 
margin of a compound eye. The antennae are usually seven-jointed. 
The labium is composed of three segments. The fore wings are larger 
than the hind wings; when at rest the wings are carried nearly 
horizontally. The venation of the wings is greatly reduced; the 
maximiun number of wing-veins found in the family is in the fore 
wings of the genus Udamoselis (Fig. 510). The three pairs of legs 
are similar in form; the tarsi are two-jointed; and each tarsus is 
furnished with a pair of claws and an empoditim or paronychium. 
The anus opens on the dorsal wall of the abdomen at some distance 
from the caudal end of the body and within a tubular structure, 
which is termed the vasiform orifice. A tongue-like organ, the lingtda, 
projects from the vasiform orifice; and at the base of the lingula 
there is a broad plate, the operculum; the anus opens beneath these 
two organs. 

In this family the type of metamorphosis corresponds quite 
closely with that known as complete metamorphosis; consequently 
the term larva is applied to the immature instars except the last, 
which is designated the pupa. 

The eggs are elongate-oval in shape and are stalked. The larvse 
during the first stadiimi are active, after which they remain quiescent. 
There are four larval and one pupal instars. The wings arise as 
histoblasts in the late embryo, and the growth of the wing-buds 
during the larval stadia takes place inside the body-wall. The 
change to the pupal instar, in which the wing-buds are external, 
takes place beneath the last larval skin, which is known as the pupa- 
case or puparium. In matiy descriptions of these insects only three 
larval instars are recognized, the fourth being described as the pupa. 
As the change to a pupa takes place beneath the last larval skin, the 
puparium, and as the adult emerges through a T-shaped opening in 
the dorsal wall of the puparium, the pupa itself is rarely observed. 

Parthenogenesis occurs in this family; but according to the 
observations of Morrill, unfertilized eggs produce only males. 

As with the adults, the anus of the immature forms opens in a 
vasiform orifice on the dorsal aspect of the body at some distance 



HOMOPTERA 



439 



from the caudal end of the body. The excrement is in the form of 
honey-dew, of which much is excreted. 

Formerly all the members of this family were included in a single 
genus, Aleyrodes; consequently, except in comparatively recent works, 
the various species are described under this generic name. In later 
days, very extended studies have been made of the family ; and the 




Fig. 511. — AsterocUton vaporariorum: a, egg; b, larva, first instar; c, puparium, 
dorsal view; d, puparium, lateral view; e, adult. (After Morrill.) 

genus Aleyrodes has been divided into many genera, which are now 
grouped into three subfamilies. The most complete systematic works 
on the family are those of Quaintance and Baker ('13 and '17). The 
following species are among our more common representatives of the 
family. 

The greenhouse white fly, Asterochiton vaporariorum. — One of 
the most important of the greenhouse pests is this insect, which infests 
very many species of plants that are grown under glass ; and some- 
times it is a serious pest in the open on tomato and other plants that 
are set out after the weather is warm. 

The adult measures about 1.5 mm. in length, and like other 
aleyrodids is covered with a white, waxy powder. The eggs are only 
.2 mm. in length, and are suspended from the leaf by a short stalk 
(Fig. 511, a). In the first instar the larva is flat, oval in outline, 
and with each margin of the body furnished with eighteen spines 
(Fig. 511, b), of which the last is much the longest. In the second 
and third instars there are only three pairs of marginal spines, a very 
small pair near the cephalic end of the body and two somewhat 
larger ones near the caudal end. The marginal fringe of wax is 



440 AN INTRODUCTION TO ENTOMOLOGY 

narrow. The puparium is box-like, the body of the insect being 
elevated on a paHsade of vertical wax rods (Fig. 511, d). There are 
other rods of wax represented in the dorsal view of the puparium 
(Fig. 511, c). 

The most successful means of destroying this pest is by fumigation 
of infested greenhouses with hydrocyanic acid gas. 

The strawberry white fly, Asterochiton packardi. — This species is 
closely allied to the greenhouse white fly, but differs in minute char- 
acters presented by the spines and wax rods of the immature forms. 
It infests strawberry plants, and is a hardy species, passing the 
winter in the egg state out of doors. 

The citrus white fly, Dialeurodes cUri. — This is a well-known pest 
in the orange-growing sections of our country, and is also found in 
greenhouses in the North. It infests all citrus fruits grown in this 
countr}^ and is found on several other plants. 

This insect injures its host in two ways: first directly, by sucking 
the sap from the leaves; and second indirectly, by furnishing nourish- 
ment, in the form of honeydew.to a fungus, the sooty mold {Meliola 
camellia), which forms a dark -brown or black membranous coating 
on the leaves and fruit, and thus interfering with the functioning of 
the leaves, retarding the ripening of the fruit, and decreasing the 
yield of the fruit. There are from two to six generations of this 
species in a year. An extended account of it is given by Morrill and 
Back('ii). 

The maple white fly, Aleurochiton Jorhesii. — Figure 509 represents 
this species, which is fairly common on maple, but rarely in sufficient 
numbers to do serious injury. 

Family COCCID^ 
The Scale-Insects or Bark-Lice, Mealy-Bugs, and others 

The family Coccidge includes the scale-insects or bark-lice, the 
mealy-bugs, and certain other insects for which there are no popular 
names. To this family belong many of the most serious pests of 
horticulturists; scarcely any kind of fruit is free from their attacks; 
and certain species of scale-insects and of mealy-bugs are constant 
pests in greenhouses. Most of the species live on the leaves and 
stems of plants; but some species infest the roots of the host-plants. 
The great majority of the species remain fixed upon their host during 
a part of their life-cycle, and can thus be transported long distances 
while 3 et alive, on fruit or on nursery stock ; this has resulted in many 
species becoming world-wide in distribution. Most of the species are 
minute or of moderate size ; but some members of the family found in 
Australia measure 25 mm. or more in length. 

While the economic importance of this family is due chiefly to 
the noxious species that belong to it, it contains several useful species. 
The most important useful species at this time is the lac-insect, 
Tachardia Idcca. The stick-lac of commerce, from which shell-lac 



HOMOPTERA 



441 



or shellac is prepared, is a resinous substance excreted by this species, 
which lives on the young branches of many tiopical trees, most of 
which belong to the genus Ficus, the figs. 

In the past, several coccids have been important as coloring agents. 
The bodies of the lac-insects, which are obtained from stick-lac in the 
manufacture of shellac, are the source of lac-dye. Another coccid, 
Kernies Uicis, which lives on a species of oak in southern Europe, 
has been used as a dye from very early times. And the well-known 




Pig. 512. — Chionaspis furfura: /, scales on pear, natural size; Ja, scale of male, 
lb, adult male, ic, scale of female, enlarged. 



cochineal is composed of the dried bodies of a coccid, Coccus cacti, 
which lives on various species of cactus. Recently these dyes have 
been largely supplanted by those obtained from coal-tar. 

China-wax is also produced by a coccid. It is the excretion of an 
insect known as pe-la, Ericerus pe-la, and was formerly much used in 
China in the manufacture of candles, before the introduction of paraffin. 

In the adult state, the two sexes of coccids differ greatly in form. 
The males are usually winged (Fig. 512); in a few species they 



442 



AN INTRODUCTION TO ENTOMOLOGY 



are either wingless or have 




vestigial wings. The fore wings 
are usually large, com- 
pared with the size of the 
body ; the hind wings are 
always greatly reduced in 
size; usually they are a 
pair of club-shaped hal- 
teres, but in a few forms 
they are more or less 
wing -like. Each hind 
Fig. 5I3-— Wing of P seudococcus . (From Patch.) ^-^^^ -g f^j-nished with a 

bristle, which is hooked at the end and fits into a pocket or fold 
on the inner margin of the fore wing of the same side; in a few spe- 
cies there are two or three or more of these hamuli. 

The venation of the fore wings is greatly reduced; a wing of 
Pseudococcus (Fig. 513) will serve to illustrate the usual type of wing- 
venation found in this family. 

The legs are wanting in many adult females, having been lost 
during the metamorphosis. In adult males they are of ordinary 
form; except in a few species, the tarsi are one-jointed, and each is 
furnished with a single claw^ Accompanying the tarsal claw there 
are often a few long, clubbed setae, the digitules (Fig. 514) ; these are 
tenent hairs ; some of the digi- 
tules arise from the tip of the ^.-—7 ^-^""X"""- — -^ d 
tarsus, and some from the 
claw. 

The caudal end of the ab- 
domen of the male usually 
bears a slender tubular pro- 
cess, the s^j'/h 5. In some spe- 
cies the stylus is as long as or even longer than the abdomen ; in others 
it is short, and in some it is apparently wanting. The stylus serves 
as a support for the penis, which is protruded from it and in some 
species is very long. 

The female coccid is always wingless, and the body is either scale- 
like or gall-like in form, or grub-like and clothed with wax. The 
waxy covering may be in the form of powder, of large tufts or plates, 
of a continuous layer, or of a thin scale, beneath which the insect lives. 

The eyes of coccids exhibit varying degrees of degeneration and 
retardation of development. The extreme of degeneration is found 
in the females, where there is only a single simple eye on each side 
of the head; this is probably a vestige of a compound eye. In the 
adult males of the more generalized forms, compound eyes are present ; 
and in some of these forms, there are also ocelli, two in some and three 
in others. When compound eyes are present the facets are usually 
large, and not closely associated. In the more specialized forms, 
instead of compound eyes there are on each lateral half of the head 
from two to eight widely separated simple eyes, which may be 
scattered vestiges of compound eyes. 




Fig. 514. — Leg of a female Lecanium: 
digitules. 



no MO PT ERA 



443 




Fig. 515. — A depigmented "acces- 
sory eye" of Psetidococcus de- 
structor: c, cornea; h, corneal 
hypodermis ; i, iris cell; r, reti- 
nal cells; n, nerve. 



The structure and development of the eyes of the male of the common mealy- 
bug, Pseudococciis (Dactylopms) destructor, was studied by Krecker ('09). In 
this insect there is on each side of the head a very small eye; since these are the 
only eyes possessed by the young nymphs, they were termed by Krecker the 
primary eyes. In the adult, in addition to the primary eyes, there are two pairs of 
eyes, one pair on the dorsal aspect of the head, and a second pair on the ventral 
aspect; these he termed the accessory eyes. 

The so-called primary eyes are very de- 
generate, in the adult at least. There is a 
lens below which there are a few retinal cells; 
but there is no corneal hypodermis, no rhab- 
doms, and no iris. 

The development of the so-called acces- 
sory eyes is greatly retarded. The histo- 
blasts from which they are developed appear 
in the latter part of the second nymphal 
stadium or in the beginning of the third; 
these are thickenings of the hypodermis. 
When fully developed as seen in the adult, 
the accessory eyes (Fig. 515) have a large 
circular cornea, followed by a comparatively 
thin layer of corneal hypodermis, encircling 
which is a single row of large iris cells. Below 
the corneal hypodermis there is a crescent- 
shaped area of polygonal rods (rhabdoms), 
which are terminally situated upon the ret- 
inal cells. From the proximal end of the 
retinal cells extend the nerve fibrils which 
join to form the optic nerve, which follows 

the contour of the head to enter the bram lateral- 
ly. Reddish brown pigment fills the retina, the iris, 
and also a ridge surrounding the eyes. There are 
no cells which function as pigment cells alone. 

The antennas of the males are lon^ and 
slender, and consist of from six to thirteen 
segments; in some of the Margarodinag they 
are branched or fiabellate. The antennce of 
adult females exhibit great variations in 
structure; they may be well developed and 
consist of as many as eleven segments; or 
they may be greatly reduced in size and in 
the number of segments; in some species 
they are either vestigial or entirely wanting 
in adult females. 

The mouth-parts are situated on the 

hind part of the ventral aspect of the head, 

and often extend caudad of the first pair of 

legs. In front of the beak there is a densely 

chitinized area, which includes the clypeus, 

Fig. 516.— Mouth-parts of a ^^gjabj^jj^ and themandibularandmaxillary 

cWtwied'Jfin ftrS^elerites. In cleared specimens there can be 

the beak; B, the beak; /, seen withm this area a complicated endo- 

labrum; 0, oesophagus; skeleton (Fig. 516, A). 

s, loop of mandibular and 'pj^g labium (Fig. 516, B), which is com- 
maxillary sete^Jn ^the^^^^^ termed the beak or rostrum, ^consists 




crumena 
lese.) 



of three segments in a few forms found in 



444 AN INTRODUCTION TO ENTOMOLOGY 

New Zealand, but usually it is more or less reduced, consisting either 
of two segments or of only one ; in a few subfamilies it is wanting 
in the adult. The mandibular and maxillary setae are wanting in 
the later nj-mphal instars of some forms, in some adult females, 
and in all adult males. These set£e, when present, are usually 
long, frequently longer than the body, and in some species sev- 
eral times as long. When not exserted, they are coiled within a 
pouch, termed the crumena, only their united tips extending to the 
labium. The crumena is a deep invagination of the body-wall, which 
extends far back into the body-cavity. Its walls are delicate, and 
not easily observed; but the coiled setae within it can be easily seen 
in cleared specimens (Fig. 516, s). 

In the classification of coccids, the characters most used are those 
presented by the female, although those of the male are used to some 
extent . The most available characters of the female are the following : 
first, the general form of the body; second, the form of the waxy 
excretions; third, the structure of the caudal end of the body; and 
fourth, the form and position of the pores through which the wax is 
excreted. 

To study the third and fourth classes of characters listed above, 
it is necessary to remove the wax, to clarify the body, and, in some 
cases, to stain it. The method most commonly used for removing the 
wax and clarifying the body is to boil the specimen in a ten per cent, 
aqueous solution of caustic potash. P'or staining the body. Gage ('19) 
found that a solution of saurefuchsin was most satisfactory; his 
formula for the preparation of this solution is as follows: 

Saurefuchsin 0-5 gf- 

Hydrochloric acid, 10% 25.0 c.c. 

Distilled water 300.0 c.c. 

The cleaned and stained 
specimens are usually mounted 
in Canada balsam for micro- 
scopic examination. 

Within the family Coccidae 
there are to be found most re- 
markable variations in struc- 
'^1 1 UTU// 1 I ture; this is especially true of 

the form of the caudal end of 
the body and of the form of the 
parts through which the wax 
and other excretions are exud- 
ed. These characters have been 
described by many authors; 
but, unfortunately, there is a 
great lack of uniformity in the 
Fig. 517. — Caudal end of female of Erzococ- terminology used by them. 
cus araucaricE: r^^n^X ring; 5, anal-ring j^^ ^j^is place, only sufficient 
setae; /, anal lobe; as, anal seta. Be- -u \ ^ u. a n 

tween the bases of the anal-ring setse space can be taken to define 
there are openings of wax-glands. the more important StfUC- 




HOMOPTERA 



445 



tures, using the terms that are more generally applied to them. 

The anal ring. — In the mealy-bugs, the tortoise-scales, and the 
lac-insects, and in the nymphs of some others, the anus is 
surrounded by a well-defined ring, the anal ring (Fig. 517, r). 

The anal-ring setce. — The anal ring bears several, from two to 
thirty but usually six, long and stout setae, the anal-ring setce (Fig. 

517.^)- 

The anal lobes. — 'In many coccids, the caudal end of the body is 
terminated by a pair of lobes, the anal lobes (Fig. 517, /). 

The anal setce. — Each anal lobe bears one or more prominent setae, 
the anal setce (Fig. 517, as). 

The anal plates. — In the subfamily Lecaniinse, the abdomen of 
the female is cleft at the caudal end, and, at the cephalic end of the 
cleft, there is a pair of tri- 
angular, or sometimes semi-cir- 
cular plates, the anal plates 
(Fig. 518, ap). 

The pygidium. — In the sub- 
family Diaspidinae, the abdo- 
men of the adult female is ter- 
minated by a strongly chi- 
tinizedunsegmented region, 
which consists of four co- 
alesced segments (Fig. 519); 
this region is termed the pygid- 
ium by writers on the Coccidae. 
This application of the term 
pygidium is quite different 
from that used in descriptions 
of other insects, where it refers 
only to the tergite of the last 
abdominal segment. A more 
detailed account of the charac- 
ters presented by the pygidium 
ofthe Diaspidinae isgiven later. 

The spines and the setce. — -The position and number of spines and 
of setae are often indicated in specific descriptions. Care should be 
taken to distinguish between these two kinds of structures. A seta 
can be recognized by the cup-like cavity in the cuticula, the alveolus, 
within which it is jointed to the body; while a spine is an outgrowth 
of the cuticula that is not separated from it by a joint. See figure 42, 
page 32. The writer in his early works on the Coccidae ('81, '82, '83) 
termed certain spine-like setae spines. 

The outlets of wax-glands. — In the Coccidae there are many minute 
openings in the cuticula through which wax is excreted; these vary 
greatly in form, in position on the body, and in the structure of the 
part of the cuticula through which they open. As the characters 
presented by these openings are much used in the classification of 
coccids, a very elaborate terminology referring to them has been 
developed. Unfortunately different authors use quite different terms, 




Fig. 518.— A 

Lecanium, 
enlarged : c^, 
anal plates. 



Fig. 519. — Adult female 
Lepidosaphes: p, py- 
gidium. 



446 



AN INTRODUCTION TO ENTOMOLOGY 



and, therefore, it is necessary to learn the terms used by an author in 
order to understand his descriptions. The most detailed and sys- 
tematic terminology that has been proposed is that of MacGillivray 
('21). Some of the many terms adopted by this author are defined 
below. 

The cerattibcB. — In the Diaspidinse and in some species of several 
other subfamilies, the terminal portion of the outlet of some of the 
wax-glands is an invaginated cuticular tube. The inner end of this 
tube is truncate, and, in the Diaspidinse, bears a perforated knob. 
This invaginated cuticular tube is termed a ceratuha. The ceratubae 
vary greatly in length and in shape; in some the greater part of the 

tube is reduced to a fine thread, 
with a bulb-like inner end. A 
few ceratubse are represented in a 
diagram given later (Fig. 522), 
The openings of most ceratubae 
are flush with the body-wall, but 
some of them open through plates 
in the marginal fringe. The dif- 
-Several types of openings of ferent types of ceratubas have re- 
ceived distinguishing names 
formed by combining a prefix with the word ceratubae. 

The cerores. — The various types of outlets of the wax-glands in 
which the cuticula is not invaginated so as to form a ceratuba are 
termed cerores. The openings of cerores through the cuticula vary 




©o 




Fig. 521. — Diagram of a pygidium of a diaspid: o, anus showing through the 
body; d, densarise; g, genacerores; i, incisions; /, first pair of lobes; pe, 
pectinas; pi, plate; 5, setas; v, vagina. 

greatly in form; several types of these openings are represented in 
Figure 520. While in most cases the openings of cerores are flush 
with the general surface of the cuticula, in some coccids (Ortheziinas) 
the cerores open through spines. There are also variations in the 
grouping of the cerores. Each of the various types has received a 
technical name formed by combining a prefix with the word cerores. 



HOMOPTERA 



447 



Thus, for example, the cerores that occur in four or five groups about 
the genital opening in many of the Diaspidinas (Fig. 52 1 , g) are temled 
genacerores. 

The features of the pygidium. — The pygidia of adult female diaspids 
present characters that are much used in distinguishing the species 
of this subfamily; among these are the following. 




Fig. 522. — A composite diagram of a pygidium: a, anus; b, marginal ceratubse, 
with elongated openings; d, ceratubae opening through plates; e, linear 
ceratubae; /, /, /, lobes; the lobes of the second and third pairs are divided. 

The position of the anus, which opens on the dorsal aspect of the 

pygidium at varying distances from the end of the body (Fig. 522,0). 

The opening of the vagina, on the ventral aspect of the pygidium 

(Fig. 521, ^0- 

The presence or absence of groups of genacerores (Fig. 521, g), the 
number of these groups when present, and the number of cerores in 
each group. The different groups are distinguished as the median 
group (niesogenacerores) , the cephalo-lateral groups, one on each side 
(pregnacerores) , and the caudo-lateral groups, one on each side 
(post genacerores), respectively. These all open on the ventral aspect 
of the pygidium. Each genaceroris has several openings. 

The position and number of openings of ceratuba?, and the t^^pes 
of ceratubae that are present (Fig. 522). 

The number of pairs of lobes borne by the margin, the shape of 
the lobes, and whether they are divided or not (Fig. 522, /, /, /). The 
pairs of lobes are numbered, beginning with the pair at the end of 
the body; in some species this pair is represented by a single lobe. 

The number of pairs of incisions {incisnrce) in the margin of the 
pygidium (Fig. 521, i). 

The presence or absence of thickenings of the margins of the 
incisions (densarice); these are thickenings of the ventral wall (Fig. 
521, d). 



448 



AN INTRODUCTION TO ENTOMOLOGY 



The presence or absence of club-shaped thickenings of the dorsal 
wall (paraphyses) that extend forward from near the bases of the 
lobes (Fig. 523. :P)- 

The presence or absence of a thickening of the lateral margin of 
the pygidium cephalad of the region in which the lobes are situated, 
and resembling the lobes in structure (Fig. 523, m). 

The nimiber and shape of the thin projections of the margin, 
known as plates. Two quite distinct types of plates can be dis- 
tinguished: in one they are broad and fringed (Fig. 521, pe); the 
plates of this type have been termed pectince; in the other type they 
are spine-like in form (Fig. $21, pi); some writers restrict the term 
plate to this type, and use pectince for the first type. Each plate 
contains the outlet of a wax-gland. 




Fig. 523. — Part of the pygidium of Chrysomphalus tenebricosus , ventral aspect, 
with the paraphyses {pp) of the dorsal wall showing through: /, /, /, lobes; 
m, thickened margin; s, spine-like setee. 

The metamorphosis of coccids. — In this family the two sexes are 
indistinguishable during the first nymphal stadium. Both are fur- 
nished with legs, antenna, and functional mouth-parts. It is during 
this period that the sedentary species spread over the plants that they 
infest. In their subsequent development the sexes differ greatly; 
hence the metamorphosis of each can be best discussed separately. 

The females never become winged. Some, as the mealy-bugs and 
Orthezia, continue active throughout their entire or almost entire life; 
but most forms become sedentary early in life and remain fixed upon 
their host. Many species lose their legs and antennas when they 
assume the quiescent form ; and in some the mandibular and maxillary 
setse are wanting in the adult. The number of n>TTiphal instars in 
females varies from two to four; the smaller number occurs in the 
more specialized subfamilies. 

In the males there are usually four njonphal instars. During the 
latter part of the nymphal life the male is quiescent, having formed a 
cocoon or a scale within or beneath which it remiains till it emerges 
as an adult. The stage of development at which the quiescent 



HOMOPTERA 449 

period begins varies greatly. Thus,- while in the mealy-bugs the 
cocoon is made during the second stadium, in I eery a it is not made till 
near the end of the third. In the Diaspidinffi the formation of the scale 
begins either at the close of the first stadium or immediately after the 
first molt. With the molt at the beginning of the quiescent period 
the male loses its legs, antennae, and mandibular and maxillary set«. 
The setcc are not replaced ; and, consequently, the adult m^ales can 
take no food. The legs and antennae of the adult are developed from 
histoblasts, as in insects with a complete metamorphosis; the wing- 
buds appear in the last nymphal stadium; but they are developed 
externally, as in insects with a gradual metamorphosis. The type of 
metamorphosis of the male coccid is, therefore, neither strictly com- 
plete nor gradual. This illustrates the difificulty of attempting to 
make sharp distinctions; for in nature all gradations exist between 
the different types of structure and of development. 

The classification of the Coccidce. — The different writers on the 
Coccidas have grouped the genera into a variable number of sub- 
families. In the classification by MacGillivray ('21), this author 
recognizes seventeen subfamilies, and gives two tables for separating 
them, one based on the characters presented by the first nymphal 
instar, and one on those of adult females. Tables are also given for 
separating the genera and species of the different subfamilies. 

The following are a few of the better-known representatives of 
this family found in this country. Several subfamilies not mentioned 
here are represented in our fauna. 

Subfamily MONOPHLEBIN^ 

The Giant Coccids 

The common name of this family 

was suggested by the large size of 
many of the exotic species. The 
best-known species found in North 
America is of moderate size ; this is 
the cottony-cushion scale, Icerya 
purchasi (Fig. 524). The adult fe- 
male measures from 4 to 8 mm. in 
length, is scale-like, dark orange- 
red, and has the dorsal surface more 
or less covered with a white or yel- 
lowish white powder. It secretes a 
large, longitudinally ribbed egg-sac, 
which is white tinged with yellow 
This beautiful insect was at one time 
the most dangerous insect pest in 
California , and did a great amount of 

injury. It is an introduced Austra- pjg ^,2^.— Icerya purchasi: females, 

lian species, and has been subdued adults, and young on orange. 




450 



AN INTRODUCTION TO ENTOMOLOGY 



to a great extent by the introduction of an Australian lady-bug, 
Roddlia cardindlis. 

Subfamily COCCIN^ 

The Cochineal Coccids 

This subfamily is of especial interest because it includes the 
cochineal insect, Coccus cacti. This is a native of Mexico, but occurs 
in the southern United States. It feeds upon various species of the 
Cactaceae. It has been extensively cultivated in India, Spain, and 
other countries. The adult female bears some resemblance to a 
mealy-bug, but differs in lacking anal lobes and an anal ring. It 
excretes a mass of white cottony threads, within which the eggs are 
laid. The dye-stuff consists of the female insects, which, when mature, 
are brushed off the plants, killed, and dried. The entire insect is used. 
Cochineal is now being superseded by aniline dyes, which are made 
from coal-tar. 



Subfamily ORTHEZIIN^ 




Fig. 525. — Orthezia, greatly 
larged. 



The Ensign Coccids 

Members of this subfamily occur 
not uncommonly on various weeds. 
They are remarkable for the sym- 
metrically arranged, glistening, white 
plates of excretion with which the body 
is clothed. Figure 525 represents a 
nymph; in the adult female, the ex- 
cretion becomes more elongated pos- 
teriorly, and forms a sac containing 
the eggs mixed with fine down. Later, 
when the young are born, they excrete 
a sufficient amount of the lamellar 
excretion to cover them. In many 
species the egg-sac is held in a more 
or less elevated position; this fact 
suggested the common name ensign- 
coccids for these insects. Most of our 
species belong to the genus Orthezia, 



Subfamily ERIOCOCCIN^ 

The Mealy-Bugs 

This subfamily includes many genera and species; the best -known 
members of it are certain mealy-bugs, which are the most common 
and noxious of greenhouse pests. These insects have received the 



HOMOPTERA 



451 





Fig. 527. — Pseiidococcus cilri. 



Fig. 526. — Pseiidococcus 
longispinosus. 



name mealy-bugs because their bodies are covered with a fine granular 

excretion, appearing as if the}' 

had been dusted with flour. 

The females are active nearly 

throughout their entire life. 

The males make a cocoon 

early in their nymphal life in 

which they remain till they 

emerge as adults. 

Figure 526 represents 
Pseiidococcus longispinosus, a 
common species in greenh ouses ; 
and Figure 527, Pseudococcits 
citri, another species that is 
found in greenhouses in the 
North. The latter species is 
also a well-known pest of 
orange trees in the South. 

Several species of mealy- 
bugs of the genus Ripersia are 
found in the nests of ants of 
the genus Lasius. 

Subfamily LECANIIN^ 

The Tortoise-Scales 

The tortoise-scales are so 
named on account of the form pig. ^28.-Lccanium hesperidum, adult fe- 



of the body in many species. males, natural size. 




452 



AN INTRODUCTION TO ENTOMOLOGY 



The most striking characteristic of this subfamily is that the abdomen 
of the female is cleft at the caudal end, and at the cephalic end of this 
cleft there is a pair of triangular or semicircular plates, the anal plates 
(Fig. 518). 

This is a large subfamily including many genera and species. 
While the various forms agree in the distinguishing characteristics 
given above, there are great differences in the appearance of the adult 
females. Many of them excrete very little wax, the body being 
practically naked, and the eggs, or the young in the viviparous species, 




Fig. 529. Saissetia olece: 
enlarged. 



I, adult females on olive, natural size; /a, female, 



are deposited beneath the body ; in other species, although the body 
is nearly naked, the adult female excretes a large, cottony egg-sac; 
and in still others the body is deeply encased in wax. 

The three following species will serve as examples of those in 
which the body is naked and which do not form an egg-sac. 

The soft scale, Lecdnium hesperidum. — This is the commonest 
and most widely spread member of this subfamily; it infests a great 
variety of plants; in the North, it is very common in greenhouses; 
in the" warmer parts of the countr}' it lives out of doors. The adult 
female is nearly flat (Fig. 528), and is viviparous. 



HOMOPTERA 



453 



The black scale, Saissetia dlece. — This is a well-known pest, es- 
pecially in California, where it infests various kinds of fruit-trees and 
other plants. The adult fe- 
male is dark brown, nearly 
black, in color; nearly hemi- 
spherical in form (Fig. 529), 
often, however, quite a little 
longer than broad. There is a 
median longitudinal ridge on 
the back, and two transverse 
ridges, the three forming a 
raised surface of the form of a 
capital H. 

The hemispherical scale, 
Saissetia hemisphcerica.— The 
adult female is nearly hemi- 
spherical in form, with the 
edges of the body flattened 
(Fig. 530). This species is 
found in conserv^atories every- 
where, and in the open air in 
warmer regions. 

Pulvindria. — Those mem- 
bers of this subfamily in which 
the adult female is nearly 
naked but excretes a large 
cottony egg-sac beneath or be- 
hind the body, are represented 
in this/ country by the genus 
Pulvinaria, of which we have 
many species. Our best-known 
species are the two following. 
The cottony maple-scale, 
Pulvindria vitis. — This species is common on maple, osage orange, 
grape, and other plants. Figure 531 represents several adult females 

with their egg-sacs on 
a cane of grape. 

The maple-leaf 
pulvinaria, Pulvindria 
acerlcola . — This 
species is also found 
on maple. It differs 
from the preceding 
Fig. 53 1 .—Pulvinaria vitir. Species in that the egg- 

sac is much longer 
than the body of the female, and is formed on the leaves instead of 
on the stem of the host. 

Ceroplastes. — In this genus the body of the female is covered with 
thick plates of wax. Alore than sixty species have been described, 




JkaraJd 

Fig. 530. — Saissetia hemispharica: 3, adult 
females on orange, natural size; 3a, 
adult female, enlarged. 




454 



AN INTRODUCTION TO ENTOMOLOGY 



several of which are found in the southern United States; the follow- 
ing will serve as an example of these beautiful insects. 

The barnacle scale, Ceropldstes cir- 
ripediformis. — Several individuals of 
this species are represented natural size, 
and one enlarged, in Figure 532. It 
infests orange, quince, and many other 
plants. 

Subfamily KERMESIIN^ 

The Pseudogall Coccids 

This subfamily includes only one 
genus, Kermes. Species of this genus 
are common on oaks wherever they 
grow. These insects are remarkable 
for the wonderful gall-like form of the 
adult females. So striking is this re- 
semblance, that they have been mis- 
taken for galls by many entomologists. 
Fig. 533 represents a species of this 
genus upon Qtiercus agrijolia. The gall- 
like bodies on the stem are adult fe- 
males, the smaller scales on the leaves 
are immature males. 

Subfamily DIASPIDIN^ 
The Armored Scales 




Fig. 532. — Ceroplastes cirripedi 
formis. 



The Diaspidinas includes those coc- 
cids that form a scale, composed in 
part of mol